Alonso went yard in the top of the ninth inning during the 7-3 win Monday at Marlins Park in Miami. Dominic Smith led off the frame with a single for the Mets. Marlins reliever Drew Steckenrider hit Juan Lagares with a pitch in the next at-bat, before striking out Brandon Nimmo.
Adam Rosario plated Smith with a single, prompting Alonso to walk to the plate. His exchange with Steckenrider lasted just one pitch.
The Marlins righty tossed a 95.3-mph fastball over the middle of the plate and Alonso sent it right back up the middle, clearing the center field fence. The homer had an exit velocity of 112.8 mph and a launch angle of 21 degrees. It also brought in three runs for the Mets.
"It's different," Mets manager Mickey Callaway told reporters, according to MLB.com. "When he hits balls like that -- whether they hit off the fence because they're not high enough to get over or they go over the fence -- watch the fielders. They all kind of just stand there like, 'What's that going to do?'
"It's a line drive, and next thing you know, it's over everybody's head. Everybody freezes because that's what you're taught in baseball: Freeze on a line drive. It's really incredible. There's just true raw power there, and it's mostly like line drives. It's crazy."
Alonso went 1-for-5 with three RBIs, two strikeouts and a run scored in the win. He is now hitting .412 on the season with six RBIs for the Mets.
The Marlins and Mets continue the three-game National League East series at 7:10 p.m. Tuesday at Marlins Park.