“I felt like a little kid,” Alonso said later. “I was just really kind of overcome with pure joy and emotion. I don’t think I’ve ever had a happier time in my life playing baseball. That’s what dreams are made of for me.”

Alonso, who went 1 for 3, drew a walk and scored two runs on Friday night, already holds several Mets records. On Aug. 27 he hit his 42nd home run to break the team’s single-season record set by Todd Hundley in 1996 and matched by Carlos Beltran in 2006. Alonso’s 22 home runs since the All-Star Game also established a club mark for most home runs in the second half of the season.

He is the first M.L.B. rookie to hit 50 home runs and 30 doubles, and only the 16th major leaguer over all to do that. Alonso expressed interest in meeting with Judge in the off-season.

“There’s nothing wrong with some friendly competition,” he said. “It’s a great thing for the city.”

With two days left in the regular season, his 52 home runs lead the majors. The closest slugger is Eugenio Suarez of the Cincinnati Reds, who has 49 . If Alonso holds his lead, he will become the first rookie in the modern era (since 1900) to be the outright home run leader. As a rookie for Brooklyn in 1906, Tim Jordan hit 12 to tie Harry Davis of the Philadelphia Athletics. In 1987, the Oakland Athletics rookie Mark McGwire hit 49 — a rookie record that would stand for 30 seasons — to match Andre Dawson of the Chicago Cubs.

Coming into this season, Alonso’s goals did not including breaking records. He simply wanted to make the team and establish himself as a contributing player. Last year in Class AA and Class AAA, he hit 36 home runs, but he was not guaranteed a place on the big-league roster this year until spring training.