Rookie phenom Bryce Harper had the game-winning walk-off single in a see-saw battle as the Washington Nationals outlasted the Mets for a 7-6 win in 12 innings on Tuesday night.

This came after New York's three errors, and a bullpen that allowed the Nats to come from behind three times.

The Mets trailed 3-0 but climbed back into the game with solo home runs from Jordany Valdespin and David Wright. Andres Torres clubbed a two-RBI double in the eighth that put New York in front 4-3.

Ian Desmond tied the game in the bottom of the inning with a hit off Mets closer Frank Francisco tp score Ryan Zimmerman, who started the inning by singling off of Tim Byrdak.

The Mets pushed ahead in the tenth inning on a lead off single from Scott Hairston, who then stole second base and moved to third on Torres' ground out. He scored on a wild-pitch by Henry Rodriguez.

Ryan Zimmerman started the bottom of the tenth with a grounder to Valdespin at shortstop, but the rookie fill-in misplayed the ball allowing Zimmerman to reach safely. Later in the inning, with runners on the corners and one out, Desmond hit a would-be game-ending double play that went through Valdespin's legs allowing the tying run to score.

In the 12th, Hairston blasted a huge go-ahead homer to put the Mets on top 6-5 before Washington rallied once again.

Michael Morse got the rally started with a double off the wall, and came around to score on another game-tying at-bat from Desmond - this time a double down the left-field line. After Met-reliever Elvin Ramirez (0-1), who was making just his second big league appearance, walked two Nationals to load the bases with two outs, Harper lined an 0-2 pitch in front of a diving Vinny Rottino in left field to end it.

Chris Young got his first start for the Mets in over 13 months after have shoulder surgery. He threw five innings, giving up three runs, two earned, on six hits.

The loss drops the Mets to 31-25, and a 1 1/2 games behind Washington in the N.L. East.