Buchholz (3-0) didn't allow a hit until Kelly Johnson led off the eighth with a broken-bat single. He retired the next three batters and reliever Andrew Miller closed the door in the ninth in a non-save situation to preserve Buchholz's third straight win to begin the season.
The right-hander, who has yielded only one run over 22 innings through the three starts, struck out 11 while working around four walks.
Napoli's two-run double in the third inning broke a scoreless tie and the Red Sox went to on to score twice more in the frame to grab control of the game, going on to even their rain-shortened three-game series.
Alex Cobb (1-1) absorbed the loss for the Rays, surrendering four runs (three earned) on seven hits over 6 2/3 innings.