ST. LOUIS -- In a suddenly revamped Marlins rotation, right-hander Trevor Richards, with all of 40 big league starts under his belt, is the elder statesman of the staff.

At age 26, Richards opened the season as the No. 2 starter, and for the most part has been a model of consistency. He turned in a gutsy 108-pitch performance on Wednesday night, giving up one run in 5 2/3 innings.

For a team looking for rotation leadership, Richards played the part. But the Cardinals were able to break through and claim a 2-1 walk-off win on Paul Goldschmidt's two-out home run off Adam Conley in the 11th inning at Busch Stadium.

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Goldschmidt's fifth career walk-off homer ended the 3-hour, 34-minute affair. Conley surrendered the homer on a 2-2 offering. Statcast projected the blast at 453 feet with a 110.2 mph exit velocity.

"They're always tough," manager Don Mattingly said after the Marlins fell to 2-5 in extra innings. "Our guys fought back, got the run late. ... Little frustrating. Especially, you get two outs, nobody on and all of a sudden, it's one pitch, game over."

The Marlins made it through the 10th inning thanks to a great escape from Sergio Romo, who inherited a first-and-third, no-out situation from Austin Brice in his second inning of relief. After Matt Carpenter was intentionally walked to load the bases, the Marlins used five infielders -- moving center fielder JT Riddle to the infield as a second shortstop up the middle. Harrison Bader struck out and Marcell Ozuna tapped into an 8-4-3 double play.

"That's where Sergio is so good, he's not going to give in," Mattingly said. "He's been there. Big spot, but he's just making pitches."

The Cardinals have taken two of three in the four-game series, which wraps up on Thursday.

More than the final result, Wednesday's game was a reminder of how much Miami is leaning on its young rotation.

"I think Trevor shows a lot," Marlins catcher Bryan Holaday said. "He's very composed out there. He's very consistent. He repeats his delivery. He's able to go out there and give us six innings, seven innings and go deep into the game. I think it's huge to have a guy like that in the middle of our rotation."

Starting pitching has been the strength of the Marlins, and through 64 games, the same starting five had stayed in order. That changed when lefty Caleb Smith (left hip inflammation) went on the injured list on June 7. Jose Urena (herniated disk) landed on the 60-day IL on June 12, and on Wednesday, Pablo Lopez (right shoulder strain) was placed on the 10-day IL.

That leaves Richards, who made his 40th big league start and 15th of the season, as the most seasoned starter on the staff. Next in line is Sandy Alcantara with 20.

"It's unfortunate that those guys are on the IL, but they'll be back, that's for sure," Richards said. "It's just one of those things. I've got to keep doing my thing, and try to help the newer guys as much as I can. I'm no veteran or anything, but I can help out a little bit here and there, and I'll do that when I can."

Richards engaged in a pitchers' duel with right-hander Daniel Ponce de Leon, who struck out six while allowing two hits with six strikeouts in six innings.

The game was scoreless until Dexter Fowler's two-out, RBI single on an elevated 90.5-mph fastball that was up and out of the strike zone. The veteran punched the ball into left field, scoring Harrison Bader, who pinch-ran after Jose Martinez singled off the wall in dead center with one out.

"We gave him a chance to get out of the sixth there," Mattingly said of Richards. "That's one thing we're trying to do, to develop these guys to have their own game. He deserved to be there at that point."

Fowler's single was a jam shot on a well-placed fastball.

"I wanted to try to jam him up and in," Richards said. "We got it there, he was able to fist it out to the outfield. That's baseball. That happens. But overall, Holly called a great game. Defense made some nice plays. It just didn't turn out how we wanted it."

Miami pulled even in the eighth on Miguel Rojas' RBI single off Carlos Martinez.

Making it three times through the order is a challenge for any pitcher, and the Marlins are challenging their youthful starters to get as deep into games as possible.

Richards nearly was able to escape the sixth. He had two outs and Bader on first before Rangel Ravelo collected his first MLB hit, a single to left, putting runners on the corners.

Pitching coach Mel Stottlemyre Jr. made a mound visit with Richards at 103 pitches. Five pitches later, Fowler delivered his run-scoring single.

Richards matched his season highs for strikeouts (eight) and pitches (108).

"His pitch count was a little higher," Mattingly said. "He had some deep counts, but you've got to pitch to get through that lineup over there. You can't just throw it over. So he had to keep mixing."