Wacha (1-0), making his third big-league start, quelled the Mets on two runs, yielding five hits and three walks en route to his initial victory. The 21-year-old right-hander struck out four.
Matt Holliday went 3-for-5 with an RBI and three runs scored while Shane Robinson added a solo homer for National League Central-leading St. Louis, which posted a win in the opener of a three-game series.
Mets starter Jeremy Hefner (1-6) allowed six runs (one earned) on eight hits in a six-inning effort.
Omar Quintanilla clouted a solo homer for New York.