Dustin Pedroia hit a two-run homer and Ryan Lavarnway added a solo shot for the Red Sox. Pedroia and Napoli both knocked in three runs to fuel the offense.
John Lackey picked up the win despite giving up six hits and five runs over five innings. He fanned three and walked two.
Daniel Descalso drove in two runs, while Kolten Wong added three hits and an RBI for the Cardinals.
Tyler Lyons was touched for five runs on as many hits in his 1 1/3 relief frames. Starter Shelby Miller worked the first 3 2/3 frames and yielded three runs and three hits with three walks.