BOSTON — Travis Shaw hit two home runs and Rusney Castillo hit one to carry Boston to a 15-1 win over the Seattle Mariners on Friday night, just hours after Red Sox Manager John Farrell announced he’s taking a medical leave to treat lymphoma.

Shaw had a two-run homer and a solo shot, and Castillo’s was a two-run homer in Boston’s highest run total of the season. The Red Sox finished with a season-high 21 hits and scored in six of the eight innings they batted.

Brock Holt and Pablo Sandoval each had three RBI with two doubles. Holt’s first drove in two runs to cap a six-run third inning.

Joe Kelly (5-6) limited the Mariners to one run and four hits in six innings. He struck out six and walked two.

Nelson Cruz went hitless in three at-bats, halting his 21-game hitting streak. It had tied Troy Tulowitzki for the majors’ longest this season.

Kyle Seager homered for Seattle, which had won eight of 12.

Mike Montgomery (4-5) gave up nine runs on 10 hits in just 2 1/3 innings.

Leading 3-1, Boston broke it open with its six-run third. Sandoval had a two-run double, Shaw followed with his two-run homer into the Red Sox bullpen, and Holt had a two-run double over the head of leaping center fielder Austin Jackson.

Holt’s second RBI double came in the fifth, Sandoval’s second run-scoring double came an inning later and Shaw homered in the eighth.

Trailing 1-0 in the first, David Ortiz had an RBI double and Castillo followed with his homer.

Seager homered in the first to put Seattle up 1-0.

NOTES: Red Sox RHP Steven Wright was placed on the seven-day concussion DL. He was hit in the neck by a batted ball during BP on Wednesday in Miami. … OF Castillo left with a bruised left foot after fouling a ball off it. … Cruz was the DH after missing the Mariners’ last game on Wednesday with neck spasms. “His neck is fine. Just going to balance it as much as I possibly can,” Manager Lloyd McClendon said.