Kip Wells gave the Reds some decent starts after joining the rotation, but this definitely wasn't one of them. Wells (2-5) lasted only two-plus innings and allowed five earned runs and five hits with one walk and one strikeout.
It wasn't a good day for the Cincinnati bullpen, which gave up eight runs. St. Louis collected 15 hits overall compared to the Reds' five.
Five straight Cardinals reached against Wells with one out in the top of the second inning, which included Troy Glaus' RBI single for the first run. Yadier Molina followed with a single, and Brendan Ryan was hit by a first-pitch breaking ball.
Next was Carpenter, who hit a first-pitch fastball to the left-field seats for a 5-0 lead.
"A couple of routine base hits and then I obviously didn't plan on Carpenter ambushing me with a grand slam," said Wells, a former Cardinals pitcher. "Having played with him, I know his offense prowess is fairly minute. It was a fastball away that he jumped on."
Wells faced two batters in the top of the third and gave up a leadoff walk and a single before he was pulled. Micah Owings tossed two scoreless innings of relief until he was roughed up in the fifth inning for four runs.
Trouble began after Owings allowed back-to-back one-out walks in the fifth. Later, with two outs, Molina and Ryan each hit soft RBI singles before Carpenter sent a two-run double into the right-field corner and made it a nine-run game.
"It's not who you would have anticipated the production coming from," Wells said of Carpenter. "What can you do?
That gave Carpenter six RBIs, which broke Gibson's 36-year-old record of five RBIs by a Cardinals pitcher. The right-hander came into the day with six RBIs -- total -- for his career.
Cincinnati began the day winners of eight of its previous nine games, 12 of 15, and 25 of 35. Carpenter came in 3-0 with a 1.57 ERA in his three previous starts vs. the Reds.
The Reds had no answers for Carpenter, who gave up only three hits and a walk with six strikeouts and was lifted after 90 pitches for postseason preservation. Owings got the Reds' first hit with a third-inning double, and Drew Stubbs followed with a single that put runners on the corners with one out.
With Drew Sutton up, Stubbs got picked off of first base by Molina's rifle arm and, although Sutton walked, the limited rally ended when Joey Votto struck out.
"We had him in a bit of trouble and then Molina picked Stubbs off, which he is known to do," Baker said. "They beat us up good today. They got every hit imaginable. It could have been worse. We popped Albert [Pujols] up with the bases loaded and nobody out. We won the series, but this kind of pollutes the series when you get beat like this."
The Reds fell to 38-40 at Great American Ball Park with three games left in the season, hosting the last-place Pirates this weekend.
"We have to win all three games to have a winning record at home, which is what you want," Baker said.