Pete Alonso stands alone among MLB rookies.

With one swing in the third inning of the Mets’ 3-0 win over the Braves on Saturday night, the slugger entered the record books as the all-time leader in homers for a rookie. Homer No. 53 moved Alonso ahead of Aaron Judge for the record.

Alonso threw his arms into the air as the ball disappeared behind the center-field fence and the theme from “The Natural” blared as he rounded the bases. The blast came on a 2-1 pitch from Braves right-hander Mike Foltynewicz in Alonso’s second at-bat of the night.

A night earlier Alonso homered to tie the record established by Judge in 2017.

Alonso’s RBI was his 120th — moving him ahead of Wally Berger for second all-time among NL rookies. Earlier this season Alonso broke Cody Bellinger’s NL record for homers by a rookie. He also shattered the Mets’ single-season record for homers, shared by Todd Hundley and Carlos Beltran.

Alonso, who won the Home Run Derby in July, met Judge at the All-Star game in Cleveland this season. The two have become entwined within the fabric of the Mets-Yankees rivalry.

“There is nothing wrong with some friendly competition, but I feel that is really good for the city and to have good players, not just here but in Queens, but to have good players over there,” Alonso said after tying the record Friday. “I feel that is a really good thing and great thing for the city.”

Alonso had to earn a spot on the Mets’ roster in spring training, but hasn’t looked back since. He was named NL Rookie of the Month in April and rolled into the All-Star game in his first season.

A history major, Alonso appreciates the magnitude of what he’s accomplished this season.

“When I think of guys in baseball history, I think of old-time guys like Lou Gehrig, Babe Ruth, Barry Bonds,” Alonso said Friday. “To think that as a rookie I hit more homers than everyone except for one guy, it’s nuts. It’s crazy.”

Now even that “one guy” has moved behind Alonso. But even Judge may have been rooting for the Mets first baseman.

“There’s no better person to represent not only the Mets, but also the City of New York,” Judge told reporters in Texas. “He’s going to do special things over his long career. It’s the first of many records he’s going to break.”

Alonso has become a popular figure among teammates in his clubhouse. Included was a special cleat he designed to commemorate 9/11. On Tuesday, Alonso will visit the 9/11 Memorial and Museum at the World Trade Center to donate his commemorative cleats.