Napoli hit a solo shot in the fourth inning and delivered a three-run blast in the seventh that ran his RBI total this season to 31 -- tops in the majors.
Boston had five homers in all while advancing the largest win total in baseball to 19. Stephen Drew contributed a two-run homer for the Red Sox in the second, Daniel Nava had a solo shot in the fourth and Mike Carp added a solo blast in the ninth.
The offensive surge made things easy for starter Clay Buchholz (6-1), who picked up the victory by throwing seven shutout innings. Buchholz gave up two hits and struck out eight.
Mark Buehrle (1-2) suffered the loss, surrendering five runs on seven hits in 6 2/3.
The win for the Red Sox completed a big night for Boston's professional teams after both the NHL's Bruins and NBA's Celtics captured their playoff games.