Seattle Mariners vs Boston Red Sox Picks and Prediction for Monday August 31 2026

The Seattle Mariners travel to Fenway Park to face the Boston Red Sox on Monday, August 31, 2026, in Boston, Massachusetts. First pitch is scheduled for 6:45 PM ET, with MLB.TV providing the coverage. Seattle enters at 64-72 overall and 27-41 on the road, while Boston is 74-62 overall and 34-32 at home. The Red Sox lead the season series 2-1 after winning the first two meetings before Seattle took the third. ESPN's Matchup Predictor gives Boston a 63.2% chance to win compared with 36.8% for Seattle. At the time of this writing the odds were not released. Before wagering on Monday's matchup, check out our free MLB picks for more baseball predictions and betting analysis.

Starting Pitchers

Seattle is scheduled to start George Kirby, who enters at 9-10 with a 4.02 ERA and 1.33 WHIP through 147.2 innings. Kirby has allowed 163 hits while recording 126 strikeouts against only 34 walks and has surrendered 17 home runs. Boston counters with Payton Tolle, who is 8-6 with a 3.09 ERA and 1.09 WHIP through 125.1 innings. Tolle has allowed 101 hits while striking out 141 against 35 walks and has surrendered 14 home runs. Boston owns the stronger statistical profile in the starting matchup, with advantages in ERA, WHIP, hits allowed and strikeout production.

Mariners Searching for an Offensive Spark

Seattle enters Monday at 64-72 and has dropped three straight games. The Mariners are 2-3 over their last five completed contests, with victories of 4-1 and 9-2 followed by losses of 6-0, 8-1 and 4-3. The recent downturn has been driven in large part by inconsistent run production.

Seattle is batting .228 as a team with 530 runs, 1,023 hits and 157 home runs. The Mariners carry a .308 on-base percentage and .374 slugging percentage. Those numbers show some power potential, but the overall batting average and on-base percentage remain weak.

The pitching staff has been more competitive. Seattle owns a 4.13 team ERA and 1.24 WHIP while allowing opponents to bat .249. The staff has issued 355 walks while recording 1,152 strikeouts. The control numbers are solid, but the team has still allowed eight or more runs in one of its last two games.

The larger concern is the road record. Seattle is only 27-41 away from home and now has to open a series at Fenway Park against a Boston club with a stronger offense and a better starting pitching matchup.

Red Sox Hold the Statistical Edge

Boston enters Monday at 74-62 and remains in the upper half of the American League East standings. The Red Sox are 2-3 over their last five completed games, with victories of 6-0 and 7-3 in 11 innings mixed around losses of 9-2, 1-0 and 4-0.

The Red Sox have been the better offensive team over the full season. Boston is batting .249 with 608 runs, 1,135 hits and 138 home runs. The club owns a .323 on-base percentage and .404 slugging percentage, giving it clear advantages over Seattle in batting average, total runs, hits, on-base percentage and slugging percentage.

Boston's pitching numbers also compare favorably. The Red Sox own a 3.48 team ERA and 1.22 WHIP while limiting opponents to a .239 batting average. They have issued 387 walks while recording 1,164 strikeouts. Compared with Seattle's 4.13 ERA, Boston has been the more reliable run-prevention team throughout the season.

The Red Sox have also already won two of the first three meetings between these clubs. Boston won 6-2 and 5-1 before Seattle answered with a 3-1 victory, meaning all three previous matchups were decided by at least two runs.

Seattle Mariners vs Boston Red Sox Picks and Prediction

Pick: Boston Red Sox Moneyline

Boston is the preferred side because it holds advantages both at the plate and in the starting matchup. The Red Sox are batting .249 compared with Seattle at .228, have scored 78 more runs and own the better team ERA. Their scheduled starter enters with a 3.09 ERA and 1.09 WHIP, while Seattle's starter carries a 4.02 ERA and 1.33 WHIP. Seattle's 27-41 road record adds another concern. With no betting line posted yet, take Boston on the moneyline once the market becomes available.

Pick: Under 8.5

The total is not yet available, but 8.5 is the preferred target number. Boston owns a 3.48 team ERA, while its scheduled starter has a 3.09 ERA and 1.09 WHIP. Seattle has also scored only four combined runs over its last three games, including one shutout loss. Boston's offense creates some risk, but the first three meetings between these teams produced totals of eight, six and four runs. Take the Under if the total is set at 8.5 or higher.

Final Picks: Boston Red Sox Moneyline and Under 8.5

This preview was completed before play on Sunday. Starting pitchers, betting lines and other game information are subject to change before the game begins.