Roger Bernadina singled and Sandy Leon reached on shortstop Ruben Tejada's fielding error to lead off the 10th against Tyler Byrdak (2-2). After Steve Lombardozzi singled to load the bases against Pedro Beato, Bryce Harper lined a hit to right field to drive in the go-ahead run.
That opened the floodgates for Washington, as Zimmerman followed by blasting a double into the right-center field gap to chase home Mark DeRosa, Lombardozzi and Harper.
The next batter, Michael Morse, belted a two-run homer to cap the outburst and send National League East-leading Washington to a victory in the first of a three-game series.
Harper finished 2-for-4 with a two-run homer in the victory.
The Mets dropped their fourth straight.