Matt Carpenter has played in 666 career games at Busch Stadium, but after his most recent one, last October, he wasn’t sure he’d ever take the field there again.

The three-time All-Star and Cardinals staple was soon to be 36 and had just finished a second straight down season, having hit just .176 with a 70 OPS-plus over 180 games from 2020-21. He had been relegated to mostly a bench role in 2021, and after the season, the Cardinals did not pick up Carpenter’s $18.5 million club option for 2022, instead paying the $2 million buyout to make him a free agent.

But Friday, Carpenter will return to St. Louis with a new lease on his career, playing a key role for the Yankees after an offseason spent revamping his swing.

“When you play for as long as I did at a place like that, you always think you’re going to finish your career there, but it just didn’t work out,” said Carpenter, who made his Cardinals debut in 2011. “As far as regrets, I have zero regrets of the way my time in St. Louis went, the memories that I made, the friendships that I made, the success that we had as a team and also that I had as individually. I raised a family there, my kids were born there. Nothing but great memories. I have nothing to be ashamed of or sad about.”

In the offseason, Carpenter went to work on his mechanics with the help of some fresh eyes, including Tim Laker (now the Dodgers’ minor league hitting coordinator), J.D. Martinez’s swing guru, Craig Wallenbrock, and former Cardinals teammate Matt Holliday, now an assistant coach at Oklahoma State.

After signing with the Yankees in late May — after asking for his release from the Rangers’ Triple-A affiliate upon being passed over for a call-up there — Carpenter has made the most of his chance and provided a surprise boost. Initially brought on as a lefty bat off the bench at a time when the Yankees were dealing with injuries, Carpenter has earned more playing time and was even reintroduced the outfield to his repertoire as a way to get his bat in the lineup.

Through 43 games entering Friday, Carpenter was batting .322 with a 242 OPS-plus and 15 home runs — more than the seven combined he had over his past two years with the Cardinals. The mustachioed veteran has become a clubhouse presence and fan favorite in The Bronx, and is returning to St. Louis a much different hitter than he was when he left.

“I was really searching the last couple years with my swing,” he said. “When you’re searching, your confidence is not very high. … That’s kind of the spot I was in the last couple seasons.

“I would have loved to have played at this level the last two seasons. I worked like crazy to do it, it just didn’t happen. For whatever reason, it’s happening now. I’m thankful for it.”

Carpenter played seven games for the 2011 Cardinals team that won the World Series, though he was not on the playoff roster. Still, he was a key part of six playoff teams — including the 2013 squad that fell to the Red Sox in the World Series — and said his favorite part about playing in St. Louis is similar to why he has enjoyed playing for the Yankees.

“Just a great culture in the clubhouse, a great atmosphere on the field, a great fan base that’s passionate and an ownership and front office that’s committed to winning,” Carpenter said. “You combine that with the history of that organization and what it means to put on that jersey — same as a New York Yankee, it’s a special thing.”

Carpenter said he still follows the Cardinals and roots for them all season, with the exception of these three games.

“Certainly looking forward to it,” Carpenter said. “Most importantly, hoping we go down there and have a great series as a club and take care of business.”