Triston Casas hit a three-run home run that helped propel the Boston Red Sox to an 8-3 victory over the visiting Seattle Mariners on Tuesday in the first matchup of a three-game series.

Casas gave Boston a 7-3 lead when he homered against reliever Trent Thornton in the seventh inning. The Red Sox received three hits from Wilyer Abreu, and two doubles and three RBIs from Alex Bregman.

Boston starting pitcher Brayan Bello (1-0) made his season debut after he missed spring training while recovering from a shoulder injury. He allowed a run on four hits in five innings, struck out three and walked three. Bello exited the mound after throwing 97 pitches.

Abreu and Ceddanne Rafaela each had two stolen bases for the Red Sox, who have won six of their last seven games.

Jorge Polanco hit his fourth home run of the season for the Mariners. J.P. Crawford collected two of Seattle’s six hits.

Seattle starter Bryce Miller (1-3) took the loss. Miller gave up four runs on five hits in 4 2/3 innings. He walked four and struck out four.

Polanco gave Seattle a 1-0 lead with his homer against Bello in the first, but Boston tied the game in the bottom half of the first when Jarren Duran tripled and scored on a Rafael Devers sacrifice fly. The triple extended Duran’s hitting streak to nine games.

Bregman’s first double drove in Rafaela and put the Red Sox in front 2-1 in the third.

Boston extended its lead to 4-1 by scoring twice in the fifth. Rafaela and Devers each walked and scored on Bregman’s second double of the game.

Crawford cut the deficit to 4-3 when his single in the sixth inning drove in Ben Williamson and Dylan Moore.

After Casas homered in the seventh, Boston added another run later in the inning when Carlos Narvaez scored on a Leo Rivas throwing error.