MIAMI -- Bottom of the ninth inning. Mets up by three runs. In comes Billy Wagner, right?

Wrong.

In a surprise development, the Mets closer was unavailable Thursday because of back spasms. Without him, the Mets bullpen squandered a three-run lead in the ninth and fell, 8-7, in 10 innings to the Marlins to suffer their sixth loss in seven games.

"It's my job," said Wagner, who's listed as day-to-day. "Like anybody else, I should be the one out there getting it done or not getting it done."

Wagner, who threw an inning of relief in Wednesday's 8-4 win at Washington, said he felt stiffness in his upper back Thursday afternoon.

"It's not got anything to do with my arm," he said.

Wagner saw a masseuse and chiropractor Thursday afternoon and said he felt good enough to pitch after playing catch in the middle innings of the game. He told manager Willie Randolph at that point that he would be available.

As the Mets staged a four-run rally in the top of the ninth to take a 7-4 lead, Wagner got up in the bullpen and threw one warm-up pitch.

"That's about as far as I got," he said.

His back tightened up again, causing Randolph to re-evaluate his options.

"We had a feeling he might not be available, so it wouldn't have changed anything," Randolph said.

Without Wagner, things deteriorated in a New York minute. Pedro Feliciano allowed a leadoff single to Jeremy Hermida. Jorge Sosa, who had thrown two innings the previous night, came in and surrendered an RBI double to Miguel Cabrera, an RBI single to Mike Jacobs and the game-tying run on a slow chopper to shortstop by Matt Treanor.

Wagner, who dealt with similar back issues recently, said he'll undergo the same treatment Friday in hopes of being available.

"Wish and hope and pray," Wagner said. "That's about all I can do."