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Terry Collins knew he was taking a risk.

With Chris Young starting his first major league game in more than a year, and a short bullpen, the New York Mets manager had few options.

Young pitched five decent innings, but Collins used every reliever he had, and rookie Elvin Ramirez allowed a game-winning single with two outs in the 12th innings to send the Mets to a 7-6 loss to the Washington Nationals on Tuesday night.

Scott Hairston hit a solo homer in the top of the 12th to give New York a 6-5 lead.

The Mets had the lead three times, and lost it all three times.

"The toughest part is the way we fought back," Collins said. "The guys played very well.

Before the game, Collins said right-hander Jon Rauch would miss all three games of the series with "debris" in his right elbow, and because he chose to give Johan Santana two days of extra rest following Friday's no-hitter, New York had just five relievers.

"We're a little short in the bullpen right now," Collins said.

The Nationals rallied when Michael Morse led off with his second double of the game, and Ian Desmond followed with another double for his third RBI.

In just his second major league game, Ramirez (0-1) walked two batters to load the bases, and a fielder's choice by Xavier Nady left the bases loaded with two outs for Harper, who lined an 0-2 pitch to left field. The ball fell just in front of a diving Vinny Rottino.

"I was trying a little bit too much," Ramirez said.

New York hopes that Jason Bay, who hasn't played since April 23, with a fractured rib, will return from his rehab assignment for Wednesday's game, but they got some more bad news when Ruben Tejada's quad strain tightened on him in a rehab game for Triple-A Buffalo. Collins said the shortstop is probably headed back for more rehabilitation in Port St. Lucie, Fla.

"We'll go out and win the next two and finish the trip strong," Collins predicted.

The Nationals are alone atop the National League East, a game ahead of Miami — which lost to Atlanta — and 1½ games ahead of the Mets.

Both managers emptied their bullpens as the game wore on. Ross Detwiler (4-3) came on in the 11th and was the Nationals' eighth pitcher.

In the 10th, both teams took advantage of miscues to score. Hairston led off with a single and later scored on a wild pitch by Henry Rodriguez — his ninth in 21 innings this season — to give the Mets a 5-4 lead.

The Nationals tied it in the bottom of the inning, thanks to two errors by shortstop Jordany Valdespin and a wild pitch by Bobby Parnell.

"It was just one of those nights, I think," Mets catcher Josh Thole said.

Ryan Zimmerman reached on one of Valdespin's errors, later took third on the wild pitch and scored on another error when Ian Desmond's grounder bounced off his glove. The Nationals loaded the bases with two outs in the inning, but Rick Ankiel struck out swinging.

The Mets fell behind 3-0 after five innings and started their comeback with solo home runs by David Wright and Valdespin in the sixth. Andres Torres hit a two-run double in the eighth to give New York a 4-3 lead.

Desmond tied the game at 4 with a run-scoring single in the eighth to set up extra innings.

Lost in the late-inning back-and-forth was the strong effort from Washington starter Jordan Zimmermann, who has pitched at least six innings in each of his 11 starts this season. Zimmermann held the Mets scoreless through five before giving up the pair of homers. He allowed five hits, struck out five, walked none and also had a single and double at the plate.

Young gave up three runs — two earned — over five innings in his first major league start since May 1, 2011. He missed most of last year because of right shoulder surgery and pitched this year in the minors.

Valdespin led off the sixth with a pinch-hit home run into the Nationals' bullpen in right field. Wright added another solo homer with two outs. It was Wright's 736th career run scored, setting a Mets franchise record.

NOTES: The Mets activated RHP Miguel Batista (lower back strain) from the 15-day DL and placed RHP Ramon Ramirez (strained right hamstring) on the 15-day DL. Ramirez injured the hamstring running in from the bullpen to join in the celebration of Santana's no-hitter last Friday, Collins said. The Mets also designated right-handed pitcher Jack Egbert for assignment.