The Boston Red Sox sit as heavy 61% moneyline favorites tonight when they welcome the Seattle Mariners to Fenway Park for a 6:45 first pitch.
Payton Tolle continues to deal, and my Mariners vs Red Sox predictions expect him to keep it rolling against an inconsistent Seattle lineup.
Find out more in my MLB picks for Monday, Aug. 31.
Who will win Mariners vs Red Sox today: Red Sox (61%)
For help understanding probabilities, see our odds calculator.
The Boston Red Sox have the more reliable pitching profile tonight with Payton Tolle in strong form. The left-hander owns a 2.99 FIP across his last two starts, and this matchup plays in his favor against a Seattle Mariners lineup that has struggled against southpaws — posting an 87 wRC+ this season.
George Kirby’s underlying metrics suggest he has pitched better than his recent results, but the right-hander has still allowed 12 earned runs over his previous three outings. That creates an opening for a Boston lineup that owns a 102 wRC+ at Fenway Park.
With Tolle trending up, the Red Sox have the cleaner edge.
Play this pick up to 62%.
COVERS INTEL: Seattle's 68 wRC+ over the last week is a whole 31 points below their season average of 99. This is a clear opportunity for Tolle to deal. 
Mariners vs Red Sox Over/Under pick: Over 7.5 (52%)
While neither lineup is absolutely flourishing right now, Kirby’s vulnerability and the bullpen profiles have me liking the Over with a low 7.5 total.
Boston’s relief corps owns a 4.71 FIP over the last week while allowing 1.30 HR/9. Seattle’s pen has not been much sharper, posting a 4.60 xERA during that same span.
This feels like the type of game where the Red Sox could do most of the scoring, but the Mariners would not need to chip in much to help push this Over.
Play this pick up to 60%.
Mariners vs Red Sox home run prediction: Julio Rodriguez (16%)
Julio Rodriguez may have just one home run over his last five games, but the underlying metrics are loud. The superstar owns a 20% barrel rate and 46.7% hard-hit rate during that span while putting 46.7% of his contact in the air.
Tolle has allowed a 48.3% fly-ball rate at home this season, and the Red Sox bullpen has also given up some home run damage lately.
With Rodriguez’s recent batted-ball profile and Fenway’s friendly left-field dimensions, there’s a real case for the slugger to leave the yard.
Play this pick up to 20%.
- ML/RL bets: 61-72, -19.23 units
- Over/Under bets: 72-57, +3.75 units
Mariners vs Red Sox weather
Weather at Fenway Park looks clean tonight, with partly cloudy skies and temperatures falling from 75°F to 70°F. Winds are light around 7–8 mph, and rain chances stay very low at 0–4%. No real delay concern, and conditions look mostly neutral for scoring.
Mariners vs Red Sox odds
- Moneyline: Mariners 40% | Red Sox 61%
- Run line: Mariners +1.5 (59%) | Red Sox -1.5 (42%)
- Over/Under: Over 7.5 (52%) | Under 7.5 (50%)
Mariners vs Red Sox trend
The Boston Red Sox have hit the moneyline in 35 of their last 50 games (+15.05 Units / 21% ROI). Find more MLB betting trends for Mariners vs. Red Sox.
How to watch Mariners vs Red Sox and game info
| Location | Fenway Park, Boston, MA |
| Date | Monday, Aug. 31, 2026 |
| First pitch | 6:45 p.m. ET |
| TV | Mariners.TV, NESN |
| Mariners starting pitcher | George Kirby (9-10, 4.02 ERA) |
| Red Sox starting pitcher | Payton Tolle (8-6, 3.09 ERA) |
Mariners vs Red Sox latest injuries
Odds are correct at the time of publishing and are subject to change.
Not intended for use in MA.
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