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Lots of missed chances and one mishandled popup led to a walkoff loss for the Washington Nationals.

Washington's hitting with men on base went from bad to worse Tuesday, and an error in the 10th inning by right fielder Jayson Werth proved costly in a 3-2 loss to the Florida Marlins.

The Nationals left 12 men on base, had another thrown out trying to score and finished 1 for 8 with runners in scoring position. Through four games they're batting .121 (4 for 33) in those situations.

"Everybody just wants to do the job right now, and maybe we're pressing a little bit," Werth said. "We just need to relax and play the game."

While the offense sputtered, it was Werth's defensive lapse that was decisive. When Omar Infante lifted a pop to short right to start Florida's 10th, Werth charged but dropped the ball, which led to the game-ending unearned run.

"Obviously that's a play that has to be made there in that spot," Werth said. "It's totally my fault."

Nationals manager Jim Riggleman said the popup handcuffed Werth.

"He really came in hard and took charge on the play," Riggleman said. "It's an error of aggression, and we can live with that."

After the miscue, Infante advanced on a wild pitch, and Hanley Ramirez was intentionally walked by Drew Storen (0-1). Gaby Sanchez's single loaded the bases before Sean Burnett took the mound, and Logan Morrison popped out and John Buck struck out.

Donnie Murphy then singled home the winning run on an 0-1 sinker.

"It wasn't a very quality pitch," Burnett said. "Unfortunately it was the worst pitch I threw all inning, and he put a good swing on it."

Edward Mujica (1-0) pitched a perfect 10th and struck out two, but before that the Nationals had lots of chances.

Two Marlins pitchers walked the bases loaded for Washington in the seventh, but Wilson Ramos grounded out to end the inning.

A baserunning mistake cost the Nationals a chance to take the lead in the eighth. With Jerry Hairston at first and two out, Werth doubled off the wall, but left fielder Morrison quickly got the ball back into the infield. Hairston took a big turn at third, then stopped and was tagged out to end the threat.

Third base coach Bo Porter took the blame.

"It was a bad read on my part," he said.

"We had a lot of base runners out there," Riggleman said. "If we keep putting them out there, we're going to get them in."

Ryan Zimmerman hit his first home run to give the Nationals a 2-1 lead in the third. Morrison hit his second homer for Florida.

Chris Coghlan, playing center field this season for the first time in his professional career, robbed the Nationals of two runs in the first inning. Coghlan sprinted into deep left center and made a leaping catch of Rick Ankiel's fly with two on and two out.

Washington's Jason Marquis allowed a baserunner in every inning he worked but gave up only two runs in 6 1-3 innings. He had two strikeouts — both called with runners in scoring position.

Starters have an ERA of 2.66 for the Nationals, but they're only 1-3.

"I prefer to look at the glass half full," Riggleman said. "I'm encouraged by the starts we've gotten."

NOTES: The Nationals' Ian Desmond and Danny Espinosa were held out of the starting lineup. Desmond is 0 for 13. ... Washington's Michael Morse has struck out six times in 13 at-bats. ... Werth went hitless against Sanchez and is 2 for 22 lifetime against him. ... RHP Chris Volstad, scheduled to start Wednesday, went 4-0 with a 5.28 ERA in five starts against Washington last year. ... Florida's Ramirez came into the series with a career average of .360 against Washington and 25 homers in 88 games.