ST. LOUIS -- The anticipated MLB debut of prospect Zac Gallen lived up to expectations. But the extra-innings hero for the Marlins was JT Riddle.

Riddle connected on a two-run home run off Andrew Miller in the 11th inning, and the Marlins pulled out a 7-6 win over the Cardinals on Thursday at Busch Stadium.

The wild game that lasted 4 hours, 31 minutes, was decided on a pickoff play at second base.

• Box score

“It was a crazy one,” Marlins manager Don Mattingly said. “The guys kept battling.”

For the second straight night, the game was decided in the 11th. This time, it was Miami that came out on top, salvaging a four-game series split. It was not without some drama, as Yadier Molina had a two-out, RBI double to make it a one-run game in the 11th. The game ended when Jack Flaherty, pinch-running for Molina, was picked off second base by closer Sergio Romo.

The Cardinals closed to within a run on Molina’s double. Jose Martinez scored from first on the play, and there was a replay challenge to see if he was safe. During the wait, Flaherty, a pitcher, ran for Molina. Marlins first baseman Miguel Rojas called the pickoff play when the players were huddled watching the review. Shortstop Yadiel Rivera applied the tag for the final out.

“That's awesome,” Rivera said. “Perfect timing. We had a pitcher running at second base. He just came off the bench, fresh. Miggy [Rojas] talked about it. We put it in play,, and we got an out.”

The wild 11th included the game-winning, two-run homer by Riddle, who drove a slider to right off Miller.

“I faced him in spring,” Riddle said. “His slider is his big sweeper. It almost has to start behind you, as a lefty. Once I missed the first one, I was like, ‘Don't miss another if he leaves it over the plate.’ I put a good swing on it.”

From the Marlins’ long-term building plans, the focus of the night was Gallen.

After posting some of the most impressive numbers in the Minor Leagues, the 23-year-old was promoted from Triple-A New Orleans and picked up where he had left off with the Baby Cakes. In five innings on Thursday, Gallen allowed one run on five hits while striking out six.

“It was cool,” Gallen said. “I tried to take in as much as I could, but at the same time, you're out there to do a job. It was awesome.”

Ranked by MLB Pipeline as Miami’s No. 18 prospect, Gallen was 9-1 with a 1.77 ERA, and 112 strikeouts in 91 1/3 innings.

The first batter Gallen faced, Matt Carpenter, drove a towering fly ball to left field that was caught on the warning track.

“That first one, Carpenter hit it about as far as you can without hitting it out,” Gallen said. “I said, 'Now we can go. Get through that first [inning], and settle down a little bit.’”

Gallen made it through the first inning on 20 pitches, with two strikeouts. His first MLB punch-out was of Paul DeJong, who swung through an 85.6 mph slider with the count full.

“Zac was pretty good, really,” Mattingly said. “It seemed like a lot of pitches. He had to battle to get through innings. But his first time out, basically. You go five innings, and you give up one run, and you have a chance to give up none. He battled. I thought he was fine.”

A third-round pick from the University of North Carolina by the Cardinals in 2016, Gallen was dealt to the Marlins as part of the Marcell Ozuna trade in December 2017.

Gallen stepped into the rotation for Pablo Lopez, who went on the 10-day injured list on Wednesday with a right shoulder strain.

Gallen, according to the Elias Sports Bureau, is just the third starting pitcher since 1995 to make his MLB debut against the team that drafted him. He joins Mario Ramos, who started for the Rangers at the Athletics on June 19, 2003, and Bobby Chouinard, who started for Oakland at Baltimore on May 26, 1996.

For the night, Gallen threw 99 pitches, with 61 strikes. His slider was his most often used pitch, being thrown 38 times. The right-hander went with his four-seam fastball 29 times, and averaged 92.7 mph with the pitch, and a high of 94.3 mph.

“I'm fortunate to get this opportunity to be here and be in the clubhouse with these guys,” Gallen said. “I finally got to make it a reality.”