Seattle Mariners vs Boston Red Sox Prediction 6/21/26 MLB Picks Today

The Boston Red Sox and the Seattle Mariners meet Sunday in MLB action from T-Mobile Park. We will look at this from a betting perspective and determine the best bets for this game. Here’s a Boston Red Sox vs. Seattle Mariners prediction.

Starting Pitching Matchup

The Boston Red Sox will send out Payton Tolle for the start here and Tolle is 3-4 with a 2.93 ERA and 60 strikeouts this season. Logan Gilbert will start for Seattle and is 5-4 with a 3.43 ERA and 92 strikeouts this season.

Boston Red Sox Recap

The Boston Red Sox come into this game looking to add on to their 5-1 win over the Mariners from Saturday to improve to 31-43 this season. After this series, the Red Sox will head on the road for a series against the Colorado Rockies.

Red Sox Win Back-To-Back Games

Wilyer Abreu leads the Red Sox with 76 hits including 16 doubles, a triple, 8 home runs and 34 RBIs while Trevor Story has 34 hits with 7 doubles, 3 homers and 19 RBIs and Marcelo Mayer’s added 40 hits with 7 doubles, 3 home runs and 18 RBIs as well. Roman Anthony has 25 hits with 5 doubles, a triple, a home run and 5 RBIs so far this season while Jarren Duran has 57 hits with 9 doubles, 12 home runs and 37 RBIs as well this season. Willson Contreras has added 72 hits with 11 doubles, 16 homers and 44 RBIs of his own on the year.

Seattle Mariners Recap

The Seattle Mariners come into this game looking to shake off a loss at the hands of the Red Sox last time out to sit at 39-39 this year. After this series, the Mariners will head on the road for a series against the Pittsburgh Pirates.

Mariners Drop Back-To-Back Games

Luke Raley has 14 home runs and 35 RBIs this season. Cole Young’s added 70 hits with 10 doubles, a triple, 6 home runs and 33 RBIs and Cal Raleigh has 28 hits with 4 doubles, 7 home runs and 20 RBIs as well this season. Randy Arozarena has 76 hits with 18 doubles, 7 home runs and 33 RBIs as well on the year. Josh Naylor also has 68 hits with 8 home runs and 32 RBIs as well on the year. Julio Rodriguez has also added 75 hits with 15 doubles, 13 home runs and 36 RBIs.

Boston Red Sox @ Seattle Mariners Betting Trends: June 21, 2026

• Probable Starting Pitcher: Logan Gilbert      Record this season: 5-4      ERA: 3.43
• Home Record: 4-3
• Last 5 against Red Sox: 0-2

Why the Seattle Mariners will win

• The Mariners have won 12 of their last 14 games against the Red Sox following a home loss.
• The Red Sox have lost five of their last six day games against AL West opponents.
• The Mariners have covered the run line in each of their last four day games against American League opponents.
• The Red Sox have failed to cover the run line in five of their last six day games against AL West opponents.
• The Red Sox have lost the first inning in five of their last six road games against AL West opponents.
• The Red Sox have trailed after 5 innings in five of their last six day games.
• The Mariners have led after 3 innings in 11 of their last 12 day games against American League opponents that held a losing record.

• Probable Starting Pitcher: Payton Tolle      Record this season: 3-4      ERA: 2.93
• Road Record: 2-2
• Last 5 against Mariners: –

Why the Boston Red Sox will win

• The underdogs have won each of the Red Sox’s last four games.
• The Mariners have lost four of their last five games as favorites after playing the previous day.
• The road team has covered the run line in each of the Red Sox’s last six games.
• The Mariners have failed to cover the run line in each of their last six Sunday games as favorites.
• The Red Sox have led after 5 innings in five of their last six games at T-Mobile Park.

Total Runs Facts

• Four of the Red Sox’s last five games have gone UNDER the total runs line.
• Six of the last eight games between the Red Sox and Mariners at T-Mobile Park have gone UNDER the total runs line.
• There has been at least one run scored in the first inning in eight of the Red Sox’s last nine road games against AL West opponents.
• There has been no run scored during the first inning in each of the last four day games between the Red Sox and Mariners at T-Mobile Park.

Seattle Mariners Player Prop Facts

• Logan Gilbert has recorded a win in four of his last five home appearances against opponents that held a losing record.
• Logan Gilbert has recorded nine or more strikeouts in each of his last four appearances with the Mariners as home favorites against AL East opponents.
• Victor Robles has recorded at least one hit in each of his last 11 appearances in day games against teams that held a losing record.
• Patrick Wisdom has hit a home run in two of his last three home appearances against the Red Sox.
• Logan Gilbert is one of only six pitchers to record 90+ Strikeouts and 20 or less Walks this season.

Boston Red Sox Player Prop Facts

• Ceddanne Rafaela has recorded at least one hit in each of his last 10 appearances in day games.
• Triston Casas has hit a home run in two of his last three appearances against the Mariners.

Matchup/League Facts

• The Mariners rank 1st in the league for walks allowed this season (200).
• The Mariners rank 29th in the league for doubles this season (98).
• The Red Sox rank 30th in the league for RBIs this season (280).
• The Red Sox rank T29th in the league for runs scored this season (293).

Boston Red Sox vs. Seattle Mariners Prediction

I’m backing Boston here. So far, the Red Sox have thrown back-to-back lefties at Seattle and the Mariners have had no answer so why not one more in Tolle who has been solid for Boston this season. Gilbert’s been unusually weak at home this season and has been far better on the road which we’re not used to seeing, and I think the Red Sox get the job done here. Give me Boston.