The Cardinals rookie lost a no-hitter with one out to go in his last start against the Nationals on Sept. 24th. He carried another into the eighth inning of Game 4 of the NLDS in Pittsburgh on Monday.
A Pedro Alvarez solo home run broke it up, but Trevor Rosenthal held a a 2-1 lead in the ninth for St. Louis, who fended off elimination and tied the series 2-2.
The win forces a decisive Game 5 at Busch Stadium on Wednesday, where Adam Wainright will get the start against Gerrit Cole.
Wacha got the win after tossing 7 1/3 innings, allowing one hit and one run while striking out nine batters. He was perfect until walking Russell Martin to start the sixth.
Matt Holliday drove in the Cardinals' only runs in that same frame with a two-run, 413-foot homer to center. They mustered just three hits, while Pirates starter Charlie Morton struck out four and walked four over 5 1/3 innings.
First pitch comes at 7:07 p.m. on Wednesday.