Red Sox vs Mariners Prediction, Odds, Moneyline, Spread & Over/Under for Aug. 31

Odds updated as of 6:13 p.m.

On Monday in MLB, the Boston Red Sox are up against the Seattle Mariners.

We’ve got you covered, in terms of the most important information about this game before you take a look at the MLB odds and spreads on FanDuel Sportsbook.

• Boston Red Sox (74-63) vs. Seattle Mariners (64-73)
• Date: Monday, August 31, 2026
• Time: 6:45 p.m. ET
• Venue: Fenway Park — Boston, Massachusetts
• Coverage: NESN and Mariners.TV

• All MLB odds, betting lines and prop bets are available on FanDuel Sportsbook.
• Moneyline: BOS: (-154) | SEA: (+142)
• Spread: BOS: -1.5 (+142) | SEA: +1.5 (-172)
• Total: 7.5 — Over: (-115) | Under: (-105)

Red Sox vs Mariners Probable Starting Pitchers

Probable Pitchers: Payton Tolle (Red Sox) – 8-6, 3.09 ERA vs George Kirby (Mariners) – 9-10, 4.02 ERA

This contest’s pitching matchup is set, as the Red Sox will send Payton Tolle (8-6) to the mound, while George Kirby (9-10) will get the nod for the Mariners. Tolle’s team is 9-13-0 against the spread in his starts this season. Tolle’s team has a record of 10-5 this season when he starts and they are the favorite on the moneyline. The Mariners have an 8-17-0 record against the spread in Kirby’s starts. The Mariners were named the moneyline underdog for two Kirby starts this season — they lost both.

All MLB win probability predictions and picks are according to numberFire.
Prediction: Red Sox win (59.3%)

• The Red Sox vs Mariners moneyline has Boston as a -154 favorite, while Seattle is a +142 underdog on the road.

• The Red Sox are 1.5-run home favorites on the runline against the Mariners. The Red Sox are +142 to cover, and the Mariners are -172.

• The over/under for the Red Sox versus Mariners game on Aug. 31 has been set at 7.5, with -115 odds on the over and -105 odds on the under.

Bet on Boston Red Sox vs. Seattle Mariners on FanDuel today!

• The Red Sox have been victorious in 50, or 53.8%, of the 93 contests they have been chosen as favorites in this season.
• This season Boston has been victorious 17 times in 26 chances when named as a favorite of at least -154 on the moneyline.
• The Red Sox’s games have gone over the total in 62 of their 135 opportunities.
• The Red Sox have an against the spread mark of 66-69-0 in 135 games with a line this season.
• The Mariners have won 10 of the 30 games they were listed as the moneyline underdog this season (33.3%).
• Seattle has a 2-2 record (winning 50% of its games) when it has played as a moneyline underdog of +142 or longer.
• The Mariners have played in 135 games with an over/under set, and have combined with their opponents to go over the total 68 times (68-61-6).
• The Mariners have a 49-86-0 record against the spread this season (covering only 36.3% of the time).

Red Sox Player Leaders

• Wilyer Abreu is hitting .257 with 31 doubles, four triples, 23 home runs and 62 walks. He has an on-base percentage of .337 while slugging .469.
• Among all qualified hitters in MLB, he ranks 64th in batting average, 63rd in on-base percentage, and 34th in slugging.
• Abreu has recorded a base hit in four games in a row. In his last five games he is batting .353 with three doubles, a home run, two walks and an RBI.
• Willson Contreras has 119 hits and an OBP of .384, both of which lead the Red Sox this season. He’s batting .274 and slugging .516.
• He ranks 34th in batting average, sixth in on-base percentage and 11th in slugging among qualified hitters.
• Ceddanne Rafaela has an OPS of .764, fueled by an OBP of .318 and a team-best slugging percentage of .446 this season.
• Caleb Durbin has been key for Boston with 110 hits, an OBP of .323 plus a slugging percentage of .389.

• Randy Arozarena has racked up 128 hits with a .367 on-base percentage, leading the Mariners in both categories. He’s batting .268 and slugging .453.
• Including all the qualified hitters in the big leagues, his batting average ranks 49th, his on-base percentage is 20th, and he is 41st in slugging.
• Josh Naylor paces his team with a .366 slugging percentage. He has a batting average of .269 with an on-base percentage of .329.
• He is currently 46th in batting average, 76th in on-base percentage and 117th in slugging percentage among all qualifying hitters.
• Cole Young has 16 doubles, three triples, 16 home runs and 36 walks while batting .246.
• Julio Rodriguez is batting .244 with 18 doubles, 20 home runs and 41 walks.

• 6/21/2026: 3-1 SEA (Favorite: Mariners, Spread: -1.5, Total: 6.5, Favorite Moneyline: -126, Underdog Moneyline: +108)
• 6/20/2026: 5-1 BOS (Favorite: Mariners, Spread: -1.5, Total: 7.5, Favorite Moneyline: -122, Underdog Moneyline: +104)
• 6/19/2026: 6-2 BOS (Favorite: Mariners, Spread: -1.5, Total: 6.5, Favorite Moneyline: -112, Underdog Moneyline: -104)
• 6/18/2025: 3-1 BOS (Favorite: Red Sox, Spread: -1.5, Total: 6.5, Favorite Moneyline: -118, Underdog Moneyline: -100)
• 6/17/2025: 8-0 SEA (Favorite: Mariners, Spread: -1.5, Total: 7, Favorite Moneyline: -162, Underdog Moneyline: +136)
• 6/16/2025: 2-0 BOS (Favorite: Mariners, Spread: -1.5, Total: 7, Favorite Moneyline: -178, Underdog Moneyline: +150)
• 4/24/2025: 4-3 SEA (Favorite: Red Sox, Spread: -1.5, Total: 8, Favorite Moneyline: -180, Underdog Moneyline: +152)
• 4/23/2025: 8-5 SEA (Favorite: Red Sox, Spread: -1.5, Total: 9.5, Favorite Moneyline: -136, Underdog Moneyline: +116)
• 4/22/2025: 8-3 BOS (Favorite: Red Sox, Spread: -1.5, Total: 9.5, Favorite Moneyline: -122, Underdog Moneyline: +104)
• 7/31/2024: 3-2 BOS (Favorite: Mariners, Spread: -1.5, Total: 9.5, Favorite Moneyline: -112, Underdog Moneyline: -104)

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