McCann's blast, following Omar Infante's run-scoring single, broke open a 2-1 game in the third inning.
McCann also drove in a run with a bases-loaded walk to finish with five RBI. Matt Diaz went 3-for-4 with a homer, three RBI and three runs scored to allow the Braves to split a four-game series at Turner Field.
Derek Lowe (10-8) yielded three runs on eight hits in 5 1/3 innings of work, walking one and fanning five.
Rickie Weeks socked a pair of homers and Prince Fielder hit his 22nd round-tripper for Milwaukee.