Alonso's mammoth mash came in the top of the ninth inning during the Mets' 7-6 win on Tuesday at Petco Park in San Diego. The blast gave the Mets the go-ahead runs.
"I blacked out for a little bit," Alonso told reporters. "I just remember touching home. I don't even remember rounding the bases."
New York and San Diego were tied at 5-5 entering the ninth frame. Mets star Robinson Cano began the final inning with a single off of Padres reliever Adam Warren. Then the Mets' 24-year-old first baseman stepped into the box.
Alonso worked a 2-2 count against Warren before settling in for his fifth offering of the exchange. Warren tossed in a 91.9-mph fastball for his final pitch to Alonso. The Mets rookie crushed the pitch to left field, sending it out of the ball park at 114.7 mph, according to Statcast.
The 449-foot, two-run homer had a launch angle of 27 degrees reached a height of 97 feet, while leaving the field in 5.4 seconds.
Franmil Reyes singled in Greg Garcia to get the Padres within one run in the bottom of the inning, before Mets closer Edwin Diaz retired the Padres to pick up his ninth save of the season.
The Mets won Tuesday's game after trailing 5-2 entering the seventh frame. Alonso also started the rally with an RBI single in the seventh inning. Michale Conforto brought in Amed Rosario with a sacrifice fly fo the Mets' fourth run. Brandon Nimmo tied the score at 5-5 by plating Alonso with an RBI double in the same inning.
Alonso was 3-for-5 with four RBIs and two runs scored in the win. He is hitting .284 with 11 home runs and 31 RBIs this season.
The Mets and Padres close out their three-game series at 3:40 p.m. Wednesday in San Diego. The matchup is tied 1-1 entering the series finale.