Mariners vs Astros Prediction, Odds, Moneyline, Spread & Over/Under for Sept. 21

Odds updated as of 7:12 p.m.

The Sunday slate in MLB includes a matchup between the Seattle Mariners and the Houston Astros.

All the info you need to make smart wagers on this game at FanDuel Sportsbook can be found below. Check out all of the latest MLB betting lines here.

Mariners vs Astros Game Info

• Seattle Mariners (86-69) vs. Houston Astros (84-71)
• Date: Sunday, September 21, 2025
• Time: 7:10 p.m. ET
• Venue: Daikin Park -- Houston, Texas
• Coverage: ESPN

Mariners vs Astros Odds & Moneyline

• All MLB odds, betting lines and prop bets are available on FanDuel Sportsbook.
• Moneyline: SEA: (-148) | HOU: (+126)
• Spread: SEA: -1.5 (+105) | HOU: +1.5 (-126)
• Total: 8.5 -- Over: (-106) | Under: (-114)

Mariners vs Astros Probable Starting Pitchers

Probable Pitchers: Logan Gilbert (Mariners) - 5-6, 3.53 ERA vs Jason Alexander (Astros) - 4-1, 4.04 ERA

This contest's pitching matchup is set, as the Mariners will send Logan Gilbert (5-6) to the mound, while Jason Alexander (4-1) will take the ball for the Astros. Gilbert and his team have a record of 8-14-0 against the spread when he starts. Gilbert's team has a record of 13-5 this season when he starts and they are the favorite on the moneyline. When Alexander starts, the Astros have gone 8-3-0 against the spread. The Astros were the moneyline underdog for five Alexander starts this season -- they won each time.

Mariners vs Astros Moneyline

• Seattle is the favorite, -148 on the moneyline, while Houston is a +126 underdog despite being at home.

Mariners vs Astros Spread

• The Mariners are at the Astros and are favored by 1.5 runs (+105 to cover) on the runline. Houston is -126 to cover.

Mariners vs Astros Over/Under

• The Mariners-Astros game on Sept. 21 has been given an over/under of 8.5 runs. The over is set at -106 and the under at -114.

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Mariners vs Astros Betting Trends

• The Mariners have come away with 62 wins in the 105 contests they have been listed as the favorites in this season.
• This season Seattle has been victorious 29 times in 45 chances when named as a favorite of at least -148 on the moneyline.
• The Mariners and their opponents have hit the over in 81 of their 150 games with a total set by oddsmakers this season.
• In 150 games with a line this season, the Mariners have a mark of 67-83-0 against the spread.
• The Astros have gone 32-23 in games they were the underdog on the moneyline (winning 58.2% of those games).
• Houston has a record of 9-5 when playing as a moneyline underdog with odds of +126 or longer (64.3%).
• The Astros have played in 154 games with an over/under set, and have combined with opponents to go over the total 70 times (70-80-4).
• The Astros have a 77-77-0 record ATS this season.

Mariners Player Leaders

• Cal Raleigh leads Seattle in OBP (.361) and total hits (140) this season. He's batting .246 batting average while slugging .586.
• Among the qualifying batters in the majors, his batting average ranks 99th, his on-base percentage ranks 18th, and he is third in slugging.
• Julio Rodriguez has hit 31 homers this season while driving in 94 runs. He's batting .269 this season and slugging .477 with an on-base percentage of .321.
• He ranks 41st in batting average, 90th in on-base percentage and 33rd in slugging among qualifying hitters.
• Rodriguez heads into this game looking to extend his two-game hit streak. In his last five games he is batting .250 with a double, a home run, two walks and three RBIs.
• Josh Naylor has collected 152 base hits, an OBP of .349 and a slugging percentage of .456 this season.
• Naylor has logged a hit or more in seven straight games. During his last 10 games he is batting .366 with a double, two home runs, three walks and nine RBIs.
• Eugenio Suarez has been key for Seattle with 129 hits, an OBP of .303 plus a slugging percentage of .532.
• Suarez heads into this matchup on a two-game hitting streak. In his last five games he is hitting .350 with three doubles, two home runs, a walk and four RBIs.

Astros Player Leaders

• Jose Altuve has a .441 slugging percentage, which leads the Astros. He's batting .263 with an on-base percentage of .323.
• Including all the qualified hitters in MLB, he is 56th in batting average, 85th in on-base percentage and 64th in slugging percentage.
• Jeremy Pena's 150 hits, .363 OBP and .477 slugging percentage all lead his team. He has a batting average of .304.
• He is sixth in batting average, 16th in on-base percentage and 33rd in slugging percentage in the majors.
• Yainer Diaz has 23 doubles, a triple, 19 home runs and 20 walks while hitting .258.
• Carlos Correa has 27 doubles, 13 home runs and 41 walks while hitting .276.

Mariners vs Astros Head to Head

• 9/20/2025: 6-4 SEA (Favorite: Astros, Spread: -1.5, Total: 8, Favorite Moneyline: -108, Underdog Moneyline: -108)
• 9/19/2025: 4-0 SEA (Favorite: Astros, Spread: -1.5, Total: 7.5, Favorite Moneyline: -108, Underdog Moneyline: -108)
• 7/20/2025: 11-3 HOU (Favorite: Mariners, Spread: -1.5, Total: 6.5, Favorite Moneyline: -144, Underdog Moneyline: +122)
• 7/19/2025: 7-6 SEA (Favorite: Mariners, Spread: -1.5, Total: 8, Favorite Moneyline: -132, Underdog Moneyline: +112)
• 7/18/2025: 6-1 SEA (Favorite: Mariners, Spread: -1.5, Total: 7.5, Favorite Moneyline: -142, Underdog Moneyline: +120)
• 5/25/2025: 5-3 HOU (Favorite: Mariners, Spread: -1.5, Total: 8.5, Favorite Moneyline: -138, Underdog Moneyline: +118)
• 5/24/2025: 2-1 HOU (Favorite: Mariners, Spread: -1.5, Total: 7, Favorite Moneyline: -110, Underdog Moneyline: -106)
• 5/23/2025: 5-3 SEA (Favorite: Astros, Spread: -1.5, Total: 8.5, Favorite Moneyline: -116, Underdog Moneyline: -102)
• 5/22/2025: 9-2 HOU (Favorite: Mariners, Spread: -1.5, Total: 8, Favorite Moneyline: -132, Underdog Moneyline: +112)
• 4/9/2025: 7-6 SEA (Favorite: Astros, Spread: -1.5, Total: 7.5, Favorite Moneyline: -142, Underdog Moneyline: +120)

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