Westbrook (1-1) logged his first victory of the year with the 112-pitch performance, overcoming four walks and striking out three for his fourth career whitewash.
Carpenter went 4-for-5 with a two-run shot while Matt Adams and Carlos Beltran also each went deep with a man aboard as the Cardinals banged out 14 hits.
Adams finished with three RBI for St. Louis, which took the rubber match of a three-game set.
Reds starter Homer Bailey (1-1) was roughed up for seven runs on nine hits over five full frames, walking two batters in the loss.
Joey Votto doubled and singled for Cincinnati.
Swim Week Miami Beach 2014 [PHOTOS]