But he isn't going to brag about it.
Randal Grichuk added three hits for St. Louis, which won for the eighth time in nine games. Chicago has lost three of four.
Carpenter entered his third-inning at-bat with a 1-for-31 career slate against Arrieta. The two were college teammates at TCU. Carpenter served as a groomsman at Arrieta's wedding.
''It was great to get out there and finally have some success against him,'' Carpenter said. ''He's given me a hard time over the years, we jab back-and-forth but, I won't rub that kind of stuff in.''
Arrieta (4-3) realized that his success against Carpenter was not going to last forever.
''A hitter like that, regardless of the history - you make a mistake and they're going to make you pay for it,'' Arrieta said.
Carpenter came into the game 0 for 27 against Arrieta in the regular season and 1 for 3 in the post season. He grounded back to the mound in his first trip to the plate.
''I always kid him that I'm a .300 hitter against him in the post-season,'' Carpenter said.
Molina recorded the third multi-homer game of his career. His last came on Aug. 21, 2011 at Wrigley Field. He drilled a two-run homer off Arrieta in the second inning.
Swinging a pink bat in honor of mother's day, Molina added a solo blast off Brian Duensing in the eighth. Molina pointed to his mother, Gladys, in the stands as he headed into the dugout.
''It's special, every time you have your family and your mama here,'' Molina said. ''I got lucky and put a good swing on it.''
Wainwright (3-3) allowed four hits in a 102-pitch stint. He struck out three and walked four. Wainwright had given up four earned run in each of his last three starts.
''It's a good outing to build off,'' Wainwright said. ''I can still get better. I can still have better fastball command. It's certainly a stepping stone.''
Chicago had runners on in six of the first seven innings.
''Overall, we're not doing a good job with runners in scoring position,'' Chicago manager Joe Maddon said.
MOTHER'S DAY MANIA
A crowd of 47,925 attended the contest, the largest crowd in the history of Busch Stadium III. The three-game series drew 143,408.
MAGIC NUMBER ON HOLD
Maddon has 999 career wins in stints with Anaheim, Tampa Bay and Chicago. He is looking to become the eighth active manager to hit the 1,000-win plateau.
Cardinals: LHP Tyler Lyons was sent to Single-A Peoria on a 30-day rehabilitation assignment. He is out with a right muscle strain.
Copyright 2017 by Associated Press. Any commercial use or distribution without the express written consent of Associated Press is strictly prohibited.