| 1998-03-31 | vs CLE | 1 | L 9-10 | 0-1 | 3 | 57,822 | Randy Johnson | Charles Nagy | Jose Mesa | Tony Fossas | Michael Jackson | 9 | 10 | -1 |
| 1998-04-01 | vs CLE | 2 | L 7-9 | 0-2 | 3 | 24,523 | Jamie Moyer | Jaret Wright | Jaret Wright | Jamie Moyer | Michael Jackson | 16 | 19 | -3 |
| 1998-04-03 | vs BOS | 3 | W 11-6 | 1-2 | 3 | 27,555 | Ken Cloude | Derek Lowe | Ken Cloude | Derek Lowe | | 27 | 25 | 2 |
| 1998-04-04 | vs BOS | 4 | W 12-6 | 2-2 | 2 | 43,035 | Bill Swift | Brian Rose | Bill Swift | Brian Rose | | 39 | 31 | 8 |
| 1998-04-05 | vs BOS | 5 | L 5-10 | 2-3 | 3 | 35,143 | Randy Johnson | Bret Saberhagen | Bret Saberhagen | Randy Johnson | | 44 | 41 | 3 |
| 1998-04-06 | vs NYA | 6 | W 8-0 | 3-3 | 2 | 27,445 | Jamie Moyer | Andy Pettitte | Jamie Moyer | Andy Pettitte | | 52 | 41 | 11 |
| 1998-04-07 | vs NYA | 7 | L 7-13 | 3-4 | 3 | 28,424 | Jim Bullinger | David Wells | David Wells | Jim Bullinger | | 59 | 54 | 5 |
| 1998-04-08 | vs NYA | 8 | L 3-4 | 3-5 | 3 | 33,922 | Ken Cloude | Hideki Irabu | Graeme Lloyd | Bobby Ayala | Mike Stanton | 62 | 58 | 4 |
| 1998-04-10 | @ BOS | 9 | L 7-9 | 3-6 | 3 | 32,805 | Randy Johnson | Brian Rose | Rich Garces | Mike Timlin | | 69 | 67 | 2 |
| 1998-04-11 | @ BOS | 10 | L 0-5 | 3-7 | 3 | 32,403 | Jamie Moyer | Pedro Martinez | Pedro Martinez | Jamie Moyer | | 69 | 72 | -3 |
| 1998-04-12 | @ BOS | 11 | L 7-8 | 3-8 | 3 | 23,270 | Jeff Fassero | Tim Wakefield | John Wasdin | Heathcliff Slocumb | | 76 | 80 | -4 |
| 1998-04-13 | @ CLE | 12 | L 5-6 | 3-9 | 3 | 42,793 | Ken Cloude | Dave Burba | Dave Burba | Ken Cloude | Michael Jackson | 81 | 86 | -5 |
| 1998-04-14 | @ CLE | 13 | L 3-8 | 3-10 | 3 | 40,490 | Bill Swift | Rick Krivda | Paul Assenmacher | Heathcliff Slocumb | | 84 | 94 | -10 |
| 1998-04-15 | @ CLE | 14 | W 5-3 | 4-10 | 3 | 40,527 | Randy Johnson | Bartolo Colon | Paul Spoljaric | Paul Assenmacher | Bobby Ayala | 89 | 97 | -8 |
| 1998-04-16 | @ MIN | 15 | W 3-2 | 5-10 | 3 | 11,351 | Jamie Moyer | Mike Morgan | Mike Timlin | Rick Aguilera | Bobby Ayala | 92 | 99 | -7 |
| 1998-04-17 | @ MIN | 16 | W 11-6 | 6-10 | 3 | 18,169 | Jeff Fassero | Eric Milton | Jeff Fassero | Eric Milton | | 103 | 105 | -2 |
| 1998-04-18 | @ MIN | 17 | W 5-3 | 7-10 | 3 | 23,943 | Ken Cloude | Bob Tewksbury | Ken Cloude | Bob Tewksbury | Bobby Ayala | 108 | 108 | 0 |
| 1998-04-19 | @ MIN | 18 | W 7-4 | 8-10 | 2 | 15,124 | Bill Swift | LaTroy Hawkins | Bill Swift | LaTroy Hawkins | Mike Timlin | 115 | 112 | 3 |
| 1998-04-20 | vs KCA | 19 | W 8-7 | 9-10 | 2 | 38,345 | Randy Johnson | Chris Haney | Felipe Lira | Danny Rios | Bobby Ayala | 123 | 119 | 4 |
| 1998-04-21 | vs KCA | 20 | L 3-5 | 9-11 | 2 | 21,547 | Jamie Moyer | Tim Belcher | Brian Bevil | Tony Fossas | Jeff Montgomery | 126 | 124 | 2 |
| 1998-04-22 | vs KCA | 21 | W 11-5 | 10-11 | 2 | 22,698 | Jeff Fassero | Hipolito Pichardo | Jeff Fassero | Hipolito Pichardo | | 137 | 129 | 8 |
| 1998-04-24 | vs MIN | 22 | W 4-2 | 11-11 | 3 | 28,157 | Ken Cloude | Bob Tewksbury | Ken Cloude | Bob Tewksbury | Bobby Ayala | 141 | 131 | 10 |
| 1998-04-25 | vs MIN | 23 | L 2-8 | 11-12 | 3 | 51,880 | Bill Swift | LaTroy Hawkins | Rick Aguilera | Mike Timlin | | 143 | 139 | 4 |
| 1998-04-26 | vs MIN | 24 | L 0-2 | 11-13 | 3 | 31,732 | Jamie Moyer | Brad Radke | Brad Radke | Jamie Moyer | Rick Aguilera | 143 | 141 | 2 |
| 1998-04-28 | @ KCA | 25 | W 5-1 | 12-13 | 3 | 11,630 | Randy Johnson | Tim Belcher | Randy Johnson | Scott Service | | 148 | 142 | 6 |
| 1998-04-29 | @ NYA | 26 | L 5-8 | 12-14 | 3 | 27,949 | Jeff Fassero | David Cone | David Cone | Jeff Fassero | Mariano Rivera | 153 | 150 | 3 |
| 1998-04-30 | @ NYA | 27 | L 8-9 | 12-15 | 4 | 28,517 | Ken Cloude | David Wells | Mariano Rivera | Bobby Ayala | | 161 | 159 | 2 |
| 1998-05-01 | vs DET | 28 | L 3-17 | 12-16 | 4 | 28,827 | Bill Swift | Tim Worrell | Tim Worrell | Bill Swift | | 164 | 176 | -12 |
| 1998-05-02 | vs DET | 29 | W 4-0 | 13-16 | 4 | 48,630 | Jamie Moyer | Justin Thompson | Jamie Moyer | Justin Thompson | | 168 | 176 | -8 |
| 1998-05-03 | vs DET | 30 | W 10-6 | 14-16 | 3 | 44,488 | Randy Johnson | Frank Castillo | Randy Johnson | Frank Castillo | | 178 | 182 | -4 |
| 1998-05-05 | vs CHA | 31 | W 8-1 | 15-16 | 3 | 22,760 | Jeff Fassero | Scott Eyre | Jeff Fassero | Scott Eyre | | 186 | 183 | 3 |
| 1998-05-06 | vs CHA | 32 | W 10-9 | 16-16 | 3 | 21,243 | Ken Cloude | James Baldwin | Heathcliff Slocumb | Carlos Castillo | Bobby Ayala | 196 | 192 | 4 |
| 1998-05-07 | vs TOR | 33 | L 0-6 | 16-17 | 3 | 24,129 | Jamie Moyer | Roger Clemens | Roger Clemens | Jamie Moyer | | 196 | 198 | -2 |
| 1998-05-08 | vs TOR | 34 | W 8-3 | 17-17 | 3 | 29,920 | Randy Johnson | Woody Williams | Randy Johnson | Woody Williams | | 204 | 201 | 3 |
| 1998-05-09 | vs TOR | 35 | L 1-4 | 17-18 | 3 | 49,851 | Bill Swift | Pat Hentgen | Pat Hentgen | Bill Swift | Randy Myers | 205 | 205 | 0 |
| 1998-05-10 | vs TOR | 36 | W 3-1 | 18-18 | 3 | 39,249 | Jeff Fassero | Juan Guzman | Jeff Fassero | Juan Guzman | Bobby Ayala | 208 | 206 | 2 |
| 1998-05-12 | @ DET | 37 | W 4-2 | 19-18 | 3 | 11,659 | Jamie Moyer | Justin Thompson | Paul Spoljaric | Justin Thompson | Bobby Ayala | 212 | 208 | 4 |
| 1998-05-13 | @ DET | 38 | L 5-8 | 19-19 | 3 | 10,766 | Ken Cloude | Brian Moehler | Brian Moehler | Ken Cloude | Todd Jones | 217 | 216 | 1 |
| 1998-05-14 | @ CHA | 39 | L 3-5 | 19-20 | 3 | 15,007 | Randy Johnson | Jason Bere | Tom Fordham | Randy Johnson | Bill Simas | 220 | 221 | -1 |
| 1998-05-15 | @ CHA | 40 | L 3-6 | 19-21 | 3 | 16,127 | Bill Swift | Jaime Navarro | Jaime Navarro | Bill Swift | Keith Foulke | 223 | 227 | -4 |
| 1998-05-16 | @ TOR | 41 | W 8-1 | 20-21 | 3 | 31,121 | Jeff Fassero | Juan Guzman | Jeff Fassero | Juan Guzman | | 231 | 228 | 3 |
| 1998-05-17 | @ TOR | 42 | L 3-4 | 20-22 | 3 | 28,111 | Jamie Moyer | Erik Hanson | Dan Plesac | Heathcliff Slocumb | | 234 | 232 | 2 |
| 1998-05-18 | @ TOR | 43 | W 9-4 | 21-22 | 3 | 28,125 | Ken Cloude | Roger Clemens | Paul Spoljaric | Roger Clemens | | 243 | 236 | 7 |
| 1998-05-19 | @ TEX | 44 | L 4-10 | 21-23 | 3 | 37,258 | Randy Johnson | Rick Helling | Rick Helling | Randy Johnson | Xavier Hernandez | 247 | 246 | 1 |
| 1998-05-20 | @ TEX | 45 | L 7-8 | 21-24 | 3 | 29,454 | Bill Swift | Darren Oliver | Tim Crabtree | Mike Timlin | John Wetteland | 254 | 254 | 0 |
| 1998-05-21 | @ TEX | 46 | L 8-9 | 21-25 | 3 | 34,613 | Jeff Fassero | John Burkett | Scott Bailes | Bobby Ayala | | 262 | 263 | -1 |
| 1998-05-22 | vs TBA | 47 | L 2-5 | 21-26 | 3 | 29,522 | Jamie Moyer | Jason Johnson | Jason Johnson | Jamie Moyer | Roberto Hernandez | 264 | 268 | -4 |
| 1998-05-23 | vs TBA | 48 | L 3-6 | 21-27 | 3 | 35,819 | Ken Cloude | Tony Saunders | Esteban Yan | Bobby Ayala | Roberto Hernandez | 267 | 274 | -7 |
| 1998-05-24 | vs TBA | 49 | W 3-1 | 22-27 | 3 | 46,867 | Randy Johnson | Dennis Springer | Randy Johnson | Dennis Springer | | 270 | 275 | -5 |
| 1998-05-25 | vs BAL | 50 | W 12-4 | 23-27 | 3 | 28,375 | Bill Swift | Nerio Rodriguez | Bill Swift | Nerio Rodriguez | | 282 | 279 | 3 |
| 1998-05-26 | vs BAL | 51 | L 3-8 | 23-28 | 3 | 31,164 | Jeff Fassero | Scott Erickson | Scott Erickson | Jeff Fassero | | 285 | 287 | -2 |
| 1998-05-28 | @ TBA | 52 | W 5-2 | 24-28 | 3 | 27,017 | Jamie Moyer | Jason Johnson | Jamie Moyer | Jason Johnson | | 290 | 289 | 1 |
| 1998-05-29 | @ TBA | 53 | W 6-2 | 25-28 | 3 | 32,142 | Randy Johnson | Tony Saunders | Randy Johnson | Tony Saunders | | 296 | 291 | 5 |
| 1998-05-30 | @ TBA | 54 | L 2-5 | 25-29 | 3 | 40,212 | Ken Cloude | Dennis Springer | Dennis Springer | Ken Cloude | Roberto Hernandez | 298 | 296 | 2 |
| 1998-05-31 | @ TBA | 55 | W 11-6 | 26-29 | 3 | 35,184 | Bill Swift | Rick White | Bill Swift | Rick White | | 309 | 302 | 7 |
| 1998-06-01 | @ BAL | 56 | L 9-10 | 26-30 | 3 | 42,622 | Jeff Fassero | Richie Lewis | Alan Mills | Tony Fossas | Armando Benitez | 318 | 312 | 6 |
| 1998-06-02 | @ BAL | 57 | L 8-9 | 26-31 | 3 | 46,724 | Jamie Moyer | Doug Drabek | Norm Charlton | Bobby Ayala | | 326 | 321 | 5 |
| 1998-06-03 | vs ANA | 58 | L 1-8 | 26-32 | 3 | 24,944 | Randy Johnson | Chuck Finley | Chuck Finley | Randy Johnson | | 327 | 329 | -2 |
| 1998-06-04 | vs ANA | 59 | L 2-6 | 26-33 | 3 | 23,709 | Ken Cloude | Ken Hill | Ken Hill | Ken Cloude | Shigetoshi Hasegawa | 329 | 335 | -6 |
| 1998-06-05 | vs LAN | 60 | W 4-0 | 27-33 | 3 | 39,053 | Bill Swift | Ismael Valdez | Bill Swift | Ismael Valdez | | 333 | 335 | -2 |
| 1998-06-06 | vs LAN | 61 | L 6-10 | 27-34 | 3 | 49,559 | Jeff Fassero | Dave Mlicki | Jim Bruske | Bob Wells | Antonio Osuna | 339 | 345 | -6 |
| 1998-06-07 | vs LAN | 62 | L 4-7 | 27-35 | 3 | 41,514 | Jamie Moyer | Darren Dreifort | Darren Dreifort | Jamie Moyer | Antonio Osuna | 343 | 352 | -9 |
| 1998-06-08 | @ SFN | 63 | L 3-4 | 27-36 | 4 | 34,166 | Randy Johnson | Danny Darwin | Danny Darwin | Randy Johnson | Rich Rodriguez | 346 | 356 | -10 |
| 1998-06-09 | @ SFN | 64 | L 6-7 | 27-37 | 4 | 24,137 | Ken Cloude | Shawn Estes | John Johnstone | Ken Cloude | Robb Nen | 352 | 363 | -11 |
| 1998-06-10 | @ SFN | 65 | W 4-1 | 28-37 | 3 | 23,590 | Bill Swift | Orel Hershiser | Bill Swift | Orel Hershiser | Heathcliff Slocumb | 356 | 364 | -8 |
| 1998-06-11 | @ OAK | 66 | L 2-5 | 28-38 | 4 | 7,838 | Jeff Fassero | Mike Oquist | Mike Oquist | Jeff Fassero | Billy Taylor | 358 | 369 | -11 |
| 1998-06-12 | @ OAK | 67 | W 5-0 | 29-38 | 3 | 11,533 | Jamie Moyer | Tom Candiotti | Jamie Moyer | Tom Candiotti | | 363 | 369 | -6 |
| 1998-06-13 | @ OAK | 68 | L 3-7 | 29-39 | 4 | 21,444 | Randy Johnson | Blake Stein | Blake Stein | Randy Johnson | Mike Fetters | 366 | 376 | -10 |
| 1998-06-14 | @ OAK | 69 | L 3-4 | 29-40 | 4 | 21,503 | Ken Cloude | Jimmy Haynes | Billy Taylor | Heathcliff Slocumb | | 369 | 380 | -11 |
| 1998-06-16 | @ ANA | 70 | L 2-3 | 29-41 | 4 | 23,123 | Bill Swift | Jason Dickson | Jason Dickson | Bill Swift | Troy Percival | 371 | 383 | -12 |
| 1998-06-17 | @ ANA | 71 | L 2-4 | 29-42 | 4 | 24,800 | Jeff Fassero | Omar Olivares | Omar Olivares | Jeff Fassero | Troy Percival | 373 | 387 | -14 |
| 1998-06-18 | @ ANA | 72 | L 5-11 | 29-43 | 4 | 30,268 | Jamie Moyer | Jarrod Washburn | Jarrod Washburn | Paul Spoljaric | Rich DeLucia | 378 | 398 | -20 |
| 1998-06-19 | vs OAK | 73 | W 9-1 | 30-43 | 4 | 33,212 | Randy Johnson | Blake Stein | Randy Johnson | Blake Stein | | 387 | 399 | -12 |
| 1998-06-20 | vs OAK | 74 | L 2-6 | 30-44 | 4 | 44,597 | Ken Cloude | Jimmy Haynes | Jimmy Haynes | Ken Cloude | | 389 | 405 | -16 |
| 1998-06-21 | vs OAK | 75 | W 10-5 | 31-44 | 4 | 37,665 | Bill Swift | Mike Oquist | Bill Swift | Mike Oquist | | 399 | 410 | -11 |
| 1998-06-22 | vs SDN | 76 | L 3-5 | 31-45 | 4 | 41,571 | Jeff Fassero | Sterling Hitchcock | Dan Miceli | Jeff Fassero | Trevor Hoffman | 402 | 415 | -13 |
| 1998-06-23 | vs SDN | 77 | W 5-3 | 32-45 | 4 | 30,961 | Jamie Moyer | Joey Hamilton | Jamie Moyer | Joey Hamilton | Heathcliff Slocumb | 407 | 418 | -11 |
| 1998-06-24 | @ SDN | 78 | W 2-1 | 33-45 | 4 | 36,900 | Randy Johnson | Andy Ashby | Randy Johnson | Andy Ashby | | 409 | 419 | -10 |
| 1998-06-25 | @ SDN | 79 | L 0-6 | 33-46 | 4 | 32,626 | Ken Cloude | Mark Langston | Mark Langston | Ken Cloude | Donne Wall | 409 | 425 | -16 |
| 1998-06-26 | @ ARI | 80 | L 8-13 | 33-47 | 4 | 49,328 | Bill Swift | Jeff Suppan | Clint Sodowsky | Paul Spoljaric | | 417 | 438 | -21 |
| 1998-06-27 | @ ARI | 81 | W 6-4 | 34-47 | 4 | 48,488 | Jeff Fassero | Andy Benes | Jeff Fassero | Andy Benes | Heathcliff Slocumb | 423 | 442 | -19 |
| 1998-06-28 | @ ARI | 82 | L 2-3 | 34-48 | 4 | 47,968 | Jamie Moyer | Brian Anderson | Alan Embree | Bobby Ayala | | 425 | 445 | -20 |
| 1998-06-30 | vs COL | 83 | L 4-6 | 34-49 | 4 | 28,821 | Randy Johnson | Pedro Astacio | Pedro Astacio | Randy Johnson | Mike Munoz | 429 | 451 | -22 |
| 1998-07-01 | vs COL | 84 | W 9-5 | 35-49 | 4 | 25,551 | Ken Cloude | Mike Saipe | Ken Cloude | Mike Saipe | | 438 | 456 | -18 |
| 1998-07-02 | vs COL | 85 | W 10-3 | 36-49 | 4 | 32,523 | Bill Swift | Darryl Kile | Bill Swift | Darryl Kile | | 448 | 459 | -11 |
| 1998-07-03 | @ TEX | 86 | W 8-2 | 37-49 | 4 | 45,233 | Jeff Fassero | John Burkett | Jeff Fassero | John Burkett | | 456 | 461 | -5 |
| 1998-07-04 | @ TEX | 87 | L 2-9 | 37-50 | 4 | 46,067 | Jamie Moyer | Aaron Sele | Aaron Sele | Jamie Moyer | | 458 | 470 | -12 |
| 1998-07-05 | @ TEX | 88 | L 4-8 | 37-51 | 4 | 38,053 | Randy Johnson | Rick Helling | Xavier Hernandez | Randy Johnson | | 462 | 478 | -16 |
| 1998-07-09 | vs ANA | 89 | W 8-6 | 38-51 | 4 | 24,210 | Jeff Fassero | Omar Olivares | Jeff Fassero | Omar Olivares | Mike Timlin | 470 | 484 | -14 |
| 1998-07-10 | vs ANA | 90 | L 3-5 | 38-52 | 4 | 28,689 | Jamie Moyer | Chuck Finley | Troy Percival | Bobby Ayala | | 473 | 489 | -16 |
| 1998-07-11 | vs ANA | 91 | W 2-0 | 39-52 | 4 | 35,788 | Randy Johnson | Steve Sparks | Randy Johnson | Steve Sparks | | 475 | 489 | -14 |
| 1998-07-12 | vs ANA | 92 | L 5-8 | 39-53 | 4 | 32,797 | Bill Swift | Jason Dickson | Jason Dickson | Bill Swift | Troy Percival | 480 | 497 | -17 |
| 1998-07-13 | vs TEX | 93 | W 10-3 | 40-53 | 4 | 25,170 | Ken Cloude | Todd Van Poppel | Ken Cloude | Todd Van Poppel | | 490 | 500 | -10 |
| 1998-07-14 | vs TEX | 94 | W 6-3 | 41-53 | 4 | 25,545 | Jeff Fassero | John Burkett | Jeff Fassero | John Burkett | Mike Timlin | 496 | 503 | -7 |
| 1998-07-15 | vs MIN | 95 | W 4-1 | 42-53 | 4 | 23,250 | Jamie Moyer | LaTroy Hawkins | Jamie Moyer | LaTroy Hawkins | Mike Timlin | 500 | 504 | -4 |
| 1998-07-16 | vs MIN | 96 | W 3-0 | 43-53 | 4 | 24,974 | Randy Johnson | Brad Radke | Randy Johnson | Brad Radke | | 503 | 504 | -1 |
| 1998-07-17 | vs KCA | 97 | W 18-5 | 44-53 | 4 | 29,500 | Bill Swift | Glendon Rusch | Bill Swift | Glendon Rusch | | 521 | 509 | 12 |
| 1998-07-18 | vs KCA | 98 | W 8-5 | 45-53 | 4 | 42,633 | Ken Cloude | Hipolito Pichardo | Bobby Ayala | Scott Service | | 529 | 514 | 15 |
| 1998-07-19 | vs KCA | 99 | L 1-4 | 45-54 | 4 | 30,851 | Jeff Fassero | Tim Belcher | Tim Belcher | Jeff Fassero | Jeff Montgomery | 530 | 518 | 12 |
| 1998-07-21 | @ TBA | 100 | W 8-3 | 46-54 | 4 | 30,298 | Jamie Moyer | Wilson Alvarez | Jamie Moyer | Wilson Alvarez | | 538 | 521 | 17 |
| 1998-07-22 | @ TBA | 101 | L 5-7 | 46-55 | 4 | 31,558 | Randy Johnson | Rolando Arrojo | Albie Lopez | Randy Johnson | Roberto Hernandez | 543 | 528 | 15 |
| 1998-07-24 | @ BAL | 102 | L 4-7 | 46-56 | 4 | 48,184 | Bill Swift | Mike Mussina | Mike Mussina | Bill Swift | Armando Benitez | 547 | 535 | 12 |
| 1998-07-25 | @ BAL | 103 | W 4-2 | 47-56 | 3 | 48,365 | Jeff Fassero | Scott Kamieniecki | Jeff Fassero | Scott Kamieniecki | Mike Timlin | 551 | 537 | 14 |
| 1998-07-26 | @ BAL | 104 | W 10-4 | 48-56 | 3 | 48,199 | Jamie Moyer | Scott Erickson | Jamie Moyer | Scott Erickson | | 561 | 541 | 20 |
| 1998-07-28 | vs CLE | 105 | L 3-4 | 48-57 | 3 | 31,124 | Randy Johnson | Charles Nagy | Charles Nagy | Randy Johnson | Michael Jackson | 564 | 545 | 19 |
| 1998-07-29 | vs CLE | 106 | L 7-8 | 48-58 | 3 | 25,953 | Ken Cloude | Jaret Wright | Chad Ogea | Greg McCarthy | Michael Jackson | 571 | 553 | 18 |
| 1998-07-30 | vs CLE | 107 | L 8-9 | 48-59 | 3 | 31,081 | Bill Swift | Dave Burba | Paul Shuey | Bob Wells | | 579 | 562 | 17 |
| 1998-07-31 | vs NYA | 108 | L 3-5 | 48-60 | 4 | 43,837 | Jeff Fassero | Hideki Irabu | Hideki Irabu | Jeff Fassero | Mariano Rivera | 582 | 567 | 15 |
| 1998-08-01 | vs NYA | 109 | L 2-5 | 48-61 | 4 | 53,840 | Jamie Moyer | David Wells | David Wells | Jamie Moyer | | 584 | 572 | 12 |
| 1998-08-02 | vs NYA | 110 | W 6-3 | 49-61 | 4 | 47,872 | Paul Spoljaric | David Cone | Bob Wells | David Cone | Mike Timlin | 590 | 575 | 15 |
| 1998-08-03 | vs BOS | 111 | W 3-1 | 50-61 | 4 | 27,887 | Ken Cloude | John Wasdin | Ken Cloude | John Wasdin | Mike Timlin | 593 | 576 | 17 |
| 1998-08-04 | vs BOS | 112 | L 1-2 | 50-62 | 3 | 29,621 | Bill Swift | Steve Avery | Steve Avery | Greg McCarthy | Tom Gordon | 594 | 578 | 16 |
| 1998-08-07 | @ DET | 113 | W 6-3 | 52-62 | 3 | 0 | Jeff Fassero | Seth Greisinger | Heathcliff Slocumb | Dean Crow | Mike Timlin | 600 | 581 | 19 |
| 1998-08-07 | @ DET | 114 | W 7-1 | 52-62 | 3 | 29,039 | Jamie Moyer | Brian Moehler | Jamie Moyer | Brian Moehler | | 607 | 582 | 25 |
| 1998-08-08 | @ DET | 115 | W 9-3 | 53-62 | 3 | 37,495 | Ken Cloude | Brian Powell | Ken Cloude | Brian Powell | | 616 | 585 | 31 |
| 1998-08-09 | @ DET | 116 | W 6-3 | 54-62 | 3 | 27,987 | Bill Swift | Bryce Florie | Bob Wells | Sean Runyan | Mike Timlin | 622 | 588 | 34 |
| 1998-08-11 | @ TOR | 117 | L 4-7 | 54-63 | 3 | 33,137 | Jeff Fassero | Chris Carpenter | Chris Carpenter | Jeff Fassero | Paul Quantrill | 626 | 595 | 31 |
| 1998-08-12 | @ TOR | 118 | L 5-11 | 54-64 | 3 | 39,139 | Jamie Moyer | Kelvim Escobar | Nerio Rodriguez | Bobby Ayala | | 631 | 606 | 25 |
| 1998-08-14 | @ CHA | 119 | L 2-14 | 54-65 | 3 | 22,713 | Ken Cloude | Mike Sirotka | Mike Sirotka | Ken Cloude | | 633 | 620 | 13 |
| 1998-08-15 | @ CHA | 120 | W 13-7 | 55-65 | 3 | 21,537 | Bill Swift | Jaime Navarro | Bill Swift | Jaime Navarro | | 646 | 627 | 19 |
| 1998-08-16 | @ CHA | 121 | L 3-5 | 55-66 | 3 | 25,471 | Jeff Fassero | James Baldwin | Keith Foulke | Jeff Fassero | Bill Simas | 649 | 632 | 17 |
| 1998-08-17 | vs DET | 122 | W 3-1 | 56-66 | 3 | 38,639 | Jamie Moyer | Brian Moehler | Jamie Moyer | Brian Moehler | Mike Timlin | 652 | 633 | 19 |
| 1998-08-18 | vs DET | 123 | L 6-7 | 56-67 | 3 | 24,136 | Paul Spoljaric | Seth Greisinger | Seth Greisinger | Bobby Ayala | Todd Jones | 658 | 640 | 18 |
| 1998-08-19 | vs TOR | 124 | L 2-16 | 56-68 | 3 | 26,258 | Ken Cloude | Pat Hentgen | Pat Hentgen | Ken Cloude | Dave Stieb | 660 | 656 | 4 |
| 1998-08-20 | vs TOR | 125 | L 0-7 | 56-69 | 4 | 26,642 | Bill Swift | Roger Clemens | Roger Clemens | Bill Swift | | 660 | 663 | -3 |
| 1998-08-21 | vs CHA | 126 | W 5-4 | 57-69 | 4 | 34,421 | Jeff Fassero | Scott Eyre | Jose Paniagua | Keith Foulke | Mike Timlin | 665 | 667 | -2 |
| 1998-08-22 | vs CHA | 127 | W 5-4 | 58-69 | 4 | 43,596 | Jamie Moyer | Jim Parque | Mike Timlin | Jaime Navarro | | 670 | 671 | -1 |
| 1998-08-23 | vs CHA | 128 | W 3-2 | 59-69 | 3 | 35,159 | Paul Spoljaric | John Snyder | Paul Spoljaric | John Snyder | Jose Paniagua | 673 | 673 | 0 |
| 1998-08-24 | vs CHA | 129 | W 11-10 | 60-69 | 3 | 27,087 | Ken Cloude | Mike Sirotka | Ken Cloude | Mike Sirotka | Mike Timlin | 684 | 683 | 1 |
| 1998-08-25 | @ CLE | 130 | L 4-10 | 60-70 | 3 | 43,113 | Bill Swift | Charles Nagy | Charles Nagy | Bill Swift | | 688 | 693 | -5 |
| 1998-08-26 | @ CLE | 131 | L 3-5 | 60-71 | 3 | 43,091 | Jeff Fassero | Dave Burba | Dave Burba | Jeff Fassero | Michael Jackson | 691 | 698 | -7 |
| 1998-08-27 | @ CLE | 132 | W 10-4 | 61-71 | 3 | 43,142 | Jamie Moyer | Jaret Wright | Jamie Moyer | Jaret Wright | | 701 | 702 | -1 |
| 1998-08-28 | @ NYA | 133 | L 3-10 | 61-72 | 4 | 49,789 | Paul Spoljaric | Orlando Hernandez | Orlando Hernandez | Paul Spoljaric | | 704 | 712 | -8 |
| 1998-08-29 | @ NYA | 134 | L 6-11 | 61-73 | 4 | 55,146 | Ken Cloude | Andy Pettitte | Andy Pettitte | Ken Cloude | | 710 | 723 | -13 |
| 1998-08-30 | @ NYA | 135 | W 13-3 | 62-73 | 4 | 55,341 | Bill Swift | Hideki Irabu | Bill Swift | Hideki Irabu | | 723 | 726 | -3 |
| 1998-08-31 | @ BOS | 136 | L 1-5 | 62-74 | 4 | 28,553 | Jeff Fassero | Bret Saberhagen | Bret Saberhagen | Jeff Fassero | | 724 | 731 | -7 |
| 1998-09-01 | @ BOS | 137 | W 7-3 | 63-74 | 3 | 28,150 | Jamie Moyer | Pete Schourek | Jamie Moyer | Derek Lowe | | 731 | 734 | -3 |
| 1998-09-02 | @ BOS | 138 | L 3-7 | 63-75 | 4 | 25,813 | Mac Suzuki | Steve Avery | Tom Gordon | Bobby Ayala | | 734 | 741 | -7 |
| 1998-09-04 | vs BAL | 139 | L 1-10 | 63-76 | 4 | 27,404 | Paul Spoljaric | Juan Guzman | Juan Guzman | Paul Spoljaric | | 735 | 751 | -16 |
| 1998-09-05 | vs BAL | 140 | W 6-5 | 64-76 | 4 | 43,831 | Ken Cloude | Scott Erickson | Greg McCarthy | Armando Benitez | Mike Timlin | 741 | 756 | -15 |
| 1998-09-06 | vs BAL | 141 | L 2-5 | 64-77 | 4 | 30,285 | Jeff Fassero | Mike Mussina | Mike Mussina | Jeff Fassero | Arthur Rhodes | 743 | 761 | -18 |
| 1998-09-07 | vs BAL | 142 | W 11-1 | 65-77 | 4 | 24,229 | Jamie Moyer | Doug Drabek | Jamie Moyer | Doug Drabek | | 754 | 762 | -8 |
| 1998-09-08 | vs TBA | 143 | L 0-10 | 65-78 | 4 | 20,679 | Mac Suzuki | Wilson Alvarez | Wilson Alvarez | Mac Suzuki | | 754 | 772 | -18 |
| 1998-09-09 | vs TBA | 144 | W 5-2 | 66-78 | 3 | 22,256 | Paul Abbott | Rolando Arrojo | Paul Abbott | Rolando Arrojo | Mike Timlin | 759 | 774 | -15 |
| 1998-09-11 | @ KCA | 145 | W 6-3 | 67-79 | 4 | 0 | Jeff Fassero | Brian Barber | Jeff Fassero | Brian Barber | Mike Timlin | 765 | 777 | -12 |
| 1998-09-11 | @ KCA | 146 | L 5-8 | 67-79 | 4 | 18,874 | Ken Cloude | Kevin Appier | Kevin Appier | Bill Swift | Glendon Rusch | 770 | 785 | -15 |
| 1998-09-12 | @ KCA | 147 | L 2-5 | 67-80 | 4 | 28,091 | Jamie Moyer | Tim Belcher | Tim Belcher | Jamie Moyer | Jeff Montgomery | 772 | 790 | -18 |
| 1998-09-14 | @ MIN | 148 | W 10-3 | 68-80 | 4 | 9,711 | Mac Suzuki | Brad Radke | Mac Suzuki | Brad Radke | | 782 | 793 | -11 |
| 1998-09-15 | @ MIN | 149 | W 12-7 | 69-80 | 3 | 8,024 | Paul Abbott | Frankie Rodriguez | Paul Abbott | Frankie Rodriguez | | 794 | 800 | -6 |
| 1998-09-16 | @ OAK | 150 | W 4-1 | 70-80 | 3 | 12,371 | Jeff Fassero | Gil Heredia | Jeff Fassero | Gil Heredia | Mike Timlin | 798 | 801 | -3 |
| 1998-09-17 | @ OAK | 151 | W 8-0 | 71-80 | 3 | 11,707 | Jamie Moyer | Tom Candiotti | Jamie Moyer | Tom Candiotti | | 806 | 801 | 5 |
| 1998-09-18 | @ ANA | 152 | W 5-3 | 72-80 | 3 | 39,902 | Ken Cloude | Ken Hill | Mike Timlin | Rich DeLucia | | 811 | 804 | 7 |
| 1998-09-19 | @ ANA | 153 | L 3-5 | 72-81 | 3 | 42,833 | Mac Suzuki | Jack McDowell | Jack McDowell | Paul Spoljaric | Troy Percival | 814 | 809 | 5 |
| 1998-09-20 | @ ANA | 154 | L 1-3 | 72-82 | 3 | 42,972 | Paul Abbott | Omar Olivares | Omar Olivares | Paul Abbott | Troy Percival | 815 | 812 | 3 |
| 1998-09-21 | vs OAK | 155 | W 5-2 | 73-82 | 3 | 30,076 | Jeff Fassero | Gil Heredia | Jose Paniagua | Gil Heredia | Mike Timlin | 820 | 814 | 6 |
| 1998-09-22 | vs OAK | 156 | W 7-6 | 74-82 | 3 | 20,908 | Jamie Moyer | Jay Witasick | Jamie Moyer | Jay Witasick | Mike Timlin | 827 | 820 | 7 |
| 1998-09-23 | vs OAK | 157 | L 3-8 | 74-83 | 3 | 21,182 | Ken Cloude | Mike Oquist | T.J. Mathews | Heathcliff Slocumb | Billy Taylor | 830 | 828 | 2 |
| 1998-09-24 | vs TEX | 158 | L 3-9 | 74-84 | 3 | 22,891 | Mac Suzuki | Aaron Sele | Aaron Sele | Mac Suzuki | | 833 | 837 | -4 |
| 1998-09-25 | vs TEX | 159 | W 15-4 | 75-84 | 3 | 39,325 | Paul Abbott | Esteban Loaiza | Paul Abbott | Esteban Loaiza | | 848 | 841 | 7 |
| 1998-09-26 | vs TEX | 160 | W 5-2 | 76-84 | 3 | 33,147 | Jeff Fassero | Eric Gunderson | Jeff Fassero | Eric Gunderson | Mike Timlin | 853 | 843 | 10 |
| 1998-09-27 | vs TEX | 161 | L 6-12 | 76-85 | 3 | 37,986 | Paul Spoljaric | Jonathan Johnson | Tony Fossas | Paul Spoljaric | | 859 | 855 | 4 |