Kolten Wong's sacrifice fly to left field provided the lead.
Matt Carpenter's two-out, two-RBI double into right center field extended it.
The Cardinals lead the Brewers 3-0 after two innings.
On the seventh pitch of his at-bat, Carpenter squared up a full-count 96 mph fastball from Brewers starter Wily Peralta. Yadier Molina and Jaime Garcia (yes, the pitcher singled) scored.
Before that, Wong's fly ball scored Randal Grichuk, who led off the inning with a single to left field. The Molina double that moved Grichuk to third was a memorable one for the catcher. It was his 124th double in Busch Stadium III, which means he has hit more doubles here than anyone else.