NEW YORK -- The rookie has the record.

New York Mets slugger Pete Alonso became the first rookie in 81 years to break his team's season home run mark when he connected Tuesday night in a 5-2 loss to the Chicago Cubs.

Alonso launched his 42nd of the year on the first pitch from Yu Darvish in the fourth inning, a no-doubt drive to the opposite field that soared far beyond the fence in right and gave the Mets a 1-0 lead.

"As soon as that ball came off my bat, I knew right away," Alonso said. "It's such an amazing feeling. It's been a dream come true for me so far this year, and I just feel really blessed and honoured."

The big first baseman raised his right arm and index finger as he began rounding the bases, then flashed a bright smile in the dugout before coming out for a curtain call.

"It's just been surreal. The way that they've kind of embraced me since Day One has been extremely special. I just want to reciprocate that," Alonso said. "They've been unbelievable and they've treated me so well. It's not just the fans. I mean, it's the entire city of New York. I'm just extremely thankful."

Alonso set the Mets record with 31 games to spare. Todd Hundley in 1996 and Carlos Beltran a decade later hit 41 homers for New York.

"It's a pleasure to have a fine young player like Pete Alonso break my record," Beltran said in a statement. "I have not met Pete personally, but people have told me he plays the game with passion and doesn't give up on any at-bat. He has had great success in his first year. Again, my congrats, Pete."

Also in a statement released by the Mets, Hundley said: "To me, he's more than a power hitter, he's a pure hitter. I have seen five or six of his games and he keeps getting better and better. He has just had a tremendous year. Congrats, Pete you deserve all the records you have broken."

Johnny Rizzo was the previous major league rookie to claim sole possession of his club's home run record when he hit 23 for the Pittsburgh Pirates in 1938. Rizzo's franchise mark was matched by Hall of Famer and former Mets broadcaster Ralph Kiner in 1946.

"It's pretty special. I think that he's a special player. The way he goes about his business is unique," New York manager Mickey Callaway said about Alonso. "There's just not a ton of guys like him, and I'm proud of him."

The 24-year-old Alonso made his major league debut this season and won the All-Star Home Run Derby in Cleveland in July. He hit a combined 36 home runs in Double-A and Triple-A last year.

"When I came up and found out I made the team, I just wanted to make the biggest impact possible, 'cause I wanted to stay up here. I didn't want to do the whole up-and-down situation. I just wanted to be a focal point," Alonso said. "This is something I put a lot of work into, made a lot of sacrifices. I mean, it's not just me. This is the ultimate for every single baseball player."

Alonso and Mark McGwire are the only players in major league history to hit 42 home runs in their first 130 games.

"It's crazy to think of the small selection of people that get to actually play in the big leagues and the even smaller selection of people that get to those milestones. And it's mind-boggling," Alonso said. "I just want to keep being Pete Alonso and stay true to who I am."

"I know what I can do. I believe in myself and I know my, I guess my capability, and I just want to keep continuing to grow and mature and just help win. That's the bottom line," he added.

The Mets might not be the only team to have their home run record rewritten this season.

The Kansas City Royals record is 38 by Mike Moustakas in 2017. Jorge Soler has 36 for the Royals.