The Houston Astros host the Seattle Mariners on September 21, 2025. First pitch from Daikin Park is scheduled for 7:10 p.m. EDT; the game will be broadcast on ESPN.
The Mariners will look to complete a critical three-game sweep over the Astros Sunday evening, which would provide them with a stranglehold on the AL West entering the final week of the season. Seattle has won the first two games of the series by a combined margin of 10-4 and now holds a 91% chance of winning the division per FanGraphs.
Sunday's matchup features a quality pitching matchup, as Logan Gilbert (3.53 ERA, 5-6) will face off against Jason Alexander (4.04 ERA, 4-1), who has pitched to an ERA of 2.88 since the All-Star break.
Find my MLB betting preview and Mariners vs Astros prediction below, as well as probable pitchers, betting trends, injury reports and more.
My Mariners vs Astros Prediction
- Mariners vs Astros pick: Under 8.5 Runs
My Mariners vs Astros best bet is on the under total runs. Make sure to find the best odds by checking our live MLB odds page.
Mariners vs Astros Odds
| Mariners Odds | ||
|---|---|---|
| Spread | Total | Moneyline |
-1.5 +115 | 8.5 -105o / -115u | -140 |
| Astros Odds | ||
|---|---|---|
| Spread | Total | Moneyline |
+1.5 -135 | 8.5 -105o / -115u | +120 |
Mariners vs Astros Projected Starting Pitchers
| RHP Logan Gilbert (SEA) | Stat | RHP Jason Alexander (HOU) |
|---|---|---|
| 5-6 | W-L | 4-1 |
| 2.5 | fWAR (FanGraphs) | 0.5 |
| 3.53/2.91 | ERA /xERA | 4.04/4.44 |
| 3.24/2.82 | FIP / xFIP | 4.78/4.19 |
| 1.05 | WHIP | 1.30 |
| 27.4% | K-BB% | 11.8% |
| 40.3% | GB% | 46.6% |
| 96 | Stuff+ | 89 |
| 111 | Location+ | 103 |
Nick Martin’s Mariners vs Astros Preview
Seattle Mariners Betting Preview: Looks to Seal the AL West
In the most important series of the year, the Mariners have come up clutch with two road wins versus an Astros side that entered the series with a record of 46-32 at Daikin Park. As Seattle now owns the tiebreaker over the Astros, it in practice holds a three-game lead and will finish up the season with six straight games at home, including three versus the lowly Colorado Rockies.
FanGraphs model currently considers the Mariners the most likely World Series champion, offering them a 17.7% chance entering today's matchup. While having already essentially wrapped up the division boosts their chances, their high-quality starting rotation certainly also helps, although their chance would be downgraded to some extent if Bryan Woo's injury turned out to be significant.
After posting a 3.23 ERA across 208 and 2/3 innings of work in 2024, Gilbert has had another tremendous season, pitching to an ERA of 3.53 and an xFIP of 2.82 throughout 120 innings of work. His strikeout minus walk rate sits at 27.4% entering this matchup, and he holds a Pitching+ rating of 108.
Gilbert has been pitching at a particularly high level of late, as throughout his last five starts he's pitched to an ERA of 2.54 and holds an xFIP of 3.08. He's struck out 33.6% of batters in that span and allowed an xBA of .184. He has been much more effective when starting inside the pitcher-friendly confines of T-Mobile Park this season, but has recorded quality starts in four of his last five road games.
The quality of Seattle's bullpen is another reason it could be a tough out come the postseason, and its relief staff has remained in strong form of late, pitching to a 3.09 ERA over the last 30 days.
The Mariners have also been in great form offensively, as since August 1st they rank fourth in baseball with a wRC+ of 118. They have been slightly more productive against righties in specific in that span, hitting to a wRC+ of 120.
Houston Astros Betting Preview: Fight to Keep Wild Card Hopes Alive
The Astros will be counting on another strong start from Alexander to help turn the tides and earn a desperately needed victory in this matchup. In losing the first two games of this series, Houston has not only essentially ended any hopes of winning the division but is now tied with the scorching hot Cleveland Guardians for the final AL Wild Card spot.
While Alexander's recent underlying metrics suggest he is due for some negative regression, they still suggest he is still pitching at a very high level. Throughout his last nine starts, Alexander holds an ERA of 2.32, and he has not allowed more than three earned runs in any of those outings. He holds an xFIP of 3.59 in that span and has struck out 22.3% of batters faced.
Houston's bullpen has pitched to an ERA of 3.72 over the last 30 days and holds the 11th-best ERA in baseball this season. Though Framber Valdez only managed to record 14 outs on Saturday, the Astros bullpen is in reasonable shape from a rest perspective, and manager Joe Espada will certainly be aggressive in deploying his top arms in this important matchup with an off-day coming after this matchup.
Yordan Alvarez's recent injury couldn't have come at a worse time for both the player and team, as the dominant slugger had been in tremendous form at the time of the injury, which came right in the thick of a close division race. Since August 1st the Astros rank 23rd in wRC+ versus right-handed pitching. They also rank 20th in hard-hit rate and rank 21st in BB/K ratio in the same span.
Mariners vs Astros Prediction, Betting Analysis
While Alexander does not project to be quite as dominant as we have seen moving forward, a total of 8.5 runs still seems too high for this matchup. Alexander has been excellent the first two times through the order this season, and Espada will likely be keen to make sure all of his top relievers are used in this matchup to support Alexander.
Houston's offense has been drastically below average versus right-handed pitching recently, and that concern is obviously magnified with Alvarez out of the lineup once again. Gilbert has been in tremendous form of late, and should have a good chance of authoring another strong start in this matchup as he looks to fine-tune his game for the postseason.
At -115 or better I see value in betting this matchup to feature less than 8.5 total runs.
Pick: Under 8.5 Total Runs (-115, bet365; Play to -125)
Moneyline
My lean would be with backing Gilbert and the Mariners at -140, but see more value in backing the under.
Run Line (Spread)
As noted, my preference would be backing the Mariners if I was forced to choose a side.
Over/Under
Backing under 8.5 total runs is my favorite play from this matchup.
Mariners vs Astros Betting Trends
