Oakland’s Mitch Moreland, a former Boston Red Sox player, tips his cap to the crowd in his first at-bat, during the second inning Tuesday night in Boston. Mary Schwalm/Associated Press

BOSTON — Chris Bassitt struck out a season-high 10 over seven effective innings and the Oakland Athletics beat the Boston Red Sox 3-2 on Tuesday night in a matchup of American League division leaders.

Matt Chapman and Elvis Andrus hit RBI singles for the A’s in the seventh inning as Oakland broke a 1-all tie with two runs. Matt Olson also had an RBI single for the A’s, who opened six-game trip with a victory.

Yusmeiro Petit pitched a scoreless eighth and Jake Diekman got his fourth save despite walking two batters in the ninth.

Rafael Devers homered for Boston, which has lost two straight since winning four in a row.

Bassitt (3-2), whose previous high for the season was nine strikeouts on April 29 at Tampa Bay, allowed just three hits and two runs. He hurt himself in the first with a pair of wild pitches that helped Boston take a 1-0 lead. But he settled down nicely after J.D. Martinez’s sacrifice fly, retiring 14 straight batters before Michael Chavis singled with one out in the sixth.

Boston led 1-0 until the fourth, when Olson singled to drive in Seth Brown.

Red Sox starter Nathan Eovaldi lasted six innings, holding Oakland to one run on two hits and two walks. He struck out four before Darwinzon Hernandez took over in the seventh. After Olson drew a leadoff walk, Jed Lowrie and Chapman followed with back-to-back singles as Oakland took its first lead.

Hernandez (0-2) was replaced by Adam Ottavino with one out and runners at second and third. Boston caught a break when Sean Murphy hit a hard grounder to third and Devers came right home to catcher Christian Vazquez, who had Lowrie in a rundown and tagged him for the second out. Chapman scored on Elvis Andrus’ bloop single for a 3-1 lead.

Devers’ homer in the bottom of the seventh, his ninth of the season, pulled Boston back within a run. Fans booed when the umpire crew circled for a replay review, but the cheering resumed when replays showed the ball cleared the Green Monster before a fan touched it.

Former Red Sox first baseman Mitch Moreland, making his first appearance at Fenway Park since being traded last August, received a nice ovation from crowd of 9,264 – the first time the ballpark had 25% capacity all season. Moreland twice tipped his helmet to the fans as Vázquez called time and walked halfway to the mound before turning and applauding Moreland.

NOTES: INF Kike Hernandez (right hamstring strain) and INF Christian Arroyo (bruised left hand) could be activated from the 10-day injured list by next week, Manager Alex Cora said.