Ludwick snapped a ninth-inning tie with a three-run homer for the Padres, who snapped a three-game losing streak and remained near the top in the NL West and wild-card standings with an 8-4 victory on Saturday.
"Ryan's done that for us, he gives you a real tough at-bat in a situation like that," Cardinals manager Tony La Russa said. "It's one of his strengths and we've enjoyed it."
Will Venable and David Eckstein had three hits and an RBI apiece for the Padres, who began the day a half-game behind San Francisco in the NL West. They remained 1½ games behind Atlanta for the wild card. San Diego hasn't won in St. Louis since Aug. 7, 2007.
"They play us well," said Eckstein, the 2006 World Series MVP with the Cardinals. "Bottom line."
Ludwick and pinch-hitter Matt Stairs hit back-to-back homers off Kyle McClellan (1-4), who hadn't allowed a run in eight straight outings but faltered in his second inning after working a scoreless eighth. It was Ludwick's 20th homer, and fifth in 160 at-bats with San Diego.
"To be able to do it against your former team, it's nice," Ludwick said. "But I'm definitely not trying to show anyone up over there."
Although Ludwick is batting only .244 with the Padres, he's 5 for 11 in the first three games of a homecoming series and 10 for 21 on the first six games of a 10-game trip. His drive on an 0-1 slider had just enough to clear the left field wall.
"I know he's feeling better about his swing," manager Bud Black said. "He's got some hits here, which I think is great for his confidence. That's more like Ryan Ludwick, what we've seen the last few days.
"He has a presence to him, and I think every pitcher has to worry about the end result when he's at the plate," Black added.
Jeff Suppan allowed a run in five innings for the Cardinals, who fell 6½ games behind the Reds with 15 games to go. They've struggled offensively since trading Ludwick in a three-team deal that brought pitcher Jake Westbrook from Cleveland at the trade deadline, going 18-25.
"I don't think it has to do with me," Ludwick said. "They hit a rough stretch, we hit a rough stretch over here, too. We lost 10 in a row. It's baseball, it happens. If you guys want to say that, it's fine, but I don't look into it."
Chris Young allowed a run on four hits in four innings in his first start since the second game of the season. Out with a strained right shoulder, Young was reinstated from the 60-day disabled list and threw 69 pitches but confessed to too much nervous energy.
"I don't remember the last time I pitched with that much adrenaline," Young said. "I got to the mound and my heart was just thumping, I could feel it in my chest. I was trying to slow myself down, but I couldn't."
Venable, Miguel Tejada and Adrian Gonzalez had an RBI apiece in a three-run, six-hit seventh against three relievers to put San Diego ahead 4-2. Left fielder Matt Holliday saved a fourth run when he threw out Tejada trying to score on Ludwick's single, Holliday's team-leading seventh assist of the season.
The Cardinals tied it in the bottom of the seventh on singles by Colby Rasmus and Pedro Feliz, the first off Luke Gregerson and the second off Mike Adams (4-1).
Suppan was the stand-in starter for rookie left-hander Jaime Garcia, who has thrown 163 1-3 innings a year after elbow reconstruction and will be throttled down the rest of the way. Suppan had worked twice totaling 2 2-3 innings since his last start Sept. 1 at Houston.
"I didn't have my best command or anything like that, but I think for the most part I stayed down in the zone," Suppan said. "So I wasn't thinking I haven't started in a while."
Skip Schumaker had two hits and the heart of the Cardinals' order, Albert Pujols, Holliday and Rasmus, combined for seven walks, two hits and an RBI. St. Louis' first two runs scored on wild pitches.
NOTES: The Padres improved to 24-9 against the NL Central. ... The Cardinals recalled five players from Triple-A Memphis, a day after that team was swept in the PCL playoffs. ... LHP Trever Miller lasted one batter in his first appearance in 12 games, walking Gonzalez to open the sixth and making one attempted pickoff throw before getting removed. ... Pujols drew his major league-leading 35th intentional walk in the fifth. Gonzalez is second in the NL with 28. ... Padres LHP Joe Thatcher has allowed one run in 16 2-3 innings in his last 34 outings. ... The Padres designated RHP Cesar Carillo for assignment for the second time this month to make room for Young. Carillo, who has spent the entire year with Triple-A Portland, was with the Phillies for three days before rejoining the Padres for three days.