Cardinals closer Trevor Rosenthal took the mound for the ninth inning with a 3-1 lead and the hope of setting his club's save record (48).
Instead he surrendered a single to Shane Peterson, drilled Martin Maldonado, threw a wild pitch to put runners on third and second and walked Jonathan Lucroy to load the bases.
Then Brewers pinch-hitter Jason Rogers crushed a 425-feet grand slam to center field.
Rosenthal was pulled for Seth Maness, but the Brewers' late arriving offense stuck around.
Domingo Santana hit a three-run homer off Maness to put the Brewers ahead 8-3.