Alonso crushed an 87-mph slider from Minnesota Twins reliever Matt Magill into the Target Field stands. The 474-foot distance is the longest home run by a Mets player since 2015.
"It's not every day you connect like that," Alonso said. "That felt really good."
Alonso has a Major League-best seven home runs of at least 440 feet this season. Alonso's home run Wednesday went further than any of the 57 home runs he hit in last week's Home Run Derby.
"I still don't think it's the farthest one he'll hit," teammate Dominic Smith said. "But for him to hit one like that, it just shows what kind of power he has."
Alonso is hitting .270 with 31 home runs and 71 RBIs this season. Alonso is on pace to become the first Met since Carlos Beltran in 2006 to hit 40 home runs in a season.
The Mets' all-time single-season home run record is 41, set by Todd Hundley in 1996.
Alonso has already set a rookie franchise record with 54 extra-base hits this year.
"The sky's the limit right now," Alonso said. "I'm just looking to keep working hard and playing hard for the guys."