Pete Alonso sent an important artifact flying into the Busch Stadium crowd.

And the Mets’ star first baseman is now the center of the Cardinals’ ire as a result.

During fifth inning of the Mets’ clash against the Cardinals Friday night, Alonso — seemingly mistakenly — tossed the ball from Masyn Winn’s first-career hit into the stands.

It’s customary for opponents to make sure the other team has the ball when a player records his first-career hit in MLB, so that he can keep it.

It didn’t appear that Alonso knew it was Winn’s first-career hit.

But the Cardinals’ dugout immediately shouted their displeasure with the act, and pitcher Miles Mikolas even had to be warned by first-base umpire John Tumpane to tone it down, according to The Athletic.

A fan who caught the ball in the stands gave it to security to return to Winn.

The Mets were leading 2-0 at the time.

Winn’s hit was a chopper toward third-base that he beat out for an infield hit, with the ball being caught by a diving Alonso at first base, who then proceeded to throw the ball into the crowd.

Winn, an infielder, is currently the Cardinals’ top-ranked prospect and the No. 32-overall prospect in baseball, according to MLB pipeline.