New York's bats warmed up later in the game, erasing a five-run deficit. Right fielder Lucas Duda hit a solo shot in the sixth and second baseman Brian Bixler blasted a two-run, game-tying homer in the eighth.
Marlins prospect Christian Yelich crushed right-hander Matt Harvey's third pitch of the game over the right-field wall to give Miami a 1-0 lead. It was Yelich's first homer of the spring. He reached base all four times he came to the plate.
Harvey, who allowed one run in two innings during his Spring Training debut last Sunday against the Astros, gave up one run vs. the Marlins, scattering three hits with four strikeouts and one walk in 2 2/3 innings. He threw 49 pitches.
"Obviously the competitive edge doesn't want to give up any hits or runs or anything like that, but it's throwing certain pitches I wouldn't normally throw in certain counts," said Harvey, who posted a 2.73 ERA over 10 starts as a rookie in 2012.
Mahoney knocked his first homer of the game off right-hander Collin McHugh to begin the fourth. His two-out, three-run shot in the fifth extended the lead to 5-0, driving in Yelich and Rob Brantly.
Brantly batted third in place of Stanton, who's leaving for the World Baseball Classic on Sunday.
Marlins starter Alex Sanabia pitched two scoreless, no-hit innings in his first Grapefruit League start. He threw 28 pitches -- 16 for strikes -- with one strikeout. He previously made two relief appearances.
Held without a hit through the first four innings, the Mets collected four in the bottom half of the frame and scored two runs off right-hander Chris Hatcher.
Duda led off with a double and came home on Andrew Brown's single up the middle. With two outs, third baseman Zach Lutz drove Brown in with a single to right following a wild pitch. Duda added his first dinger of the spring against Mike Dunn in the sixth, while Lutz and catching prospect Travis d'Arnaud doubled in a three-run seventh off Miami reliever A.J. Ramos.
Up next: Right-hander Dillon Gee makes his 2013 Grapefruit League debut against the Marlins on Sunday. Last season, Gee went 6-7 with a 4.10 ERA in 17 starts. Miami counters with Nathan Eovaldi in a 1:05 p.m. ET contest. Former Marlins catcher John Buck, as well as outfielders Mike Baxter and Kirk Nieuwenheis, will make the trip.