Florida used three straight singles from Gaby Sanchez, Hanley Ramirez and DeWayne Wise to load the bases, and Stanton cracked a 3-2 cutter from Jason Isringhausen over the left field wall for his second career grand slam.
Omar Infante collected three hits, including a triple, and Sanchez added a pair of RBI for the Marlins, who have won seven of their last nine games.
Leo Nunez (1-2) gave up the lead in the ninth, but picked up the win courtesy of Stanton’s moonshot. He also absorbed his fourth blown save of the season
Isringhausen (2-1) was tagged with the loss for the Mets, who have lost three consecutive games.
Lucas Duda and Jason Bay smacked home runs for New York.