It’s all slipping away for the New York Mets again.

With a listless loss to the Florida Marlins on Friday night, New York relinquished control of its playoff fate. Now, the desperate Mets will start ace Johan Santana on three days’ rest Saturday, but they need help to reach the postseason.

Mike Pelfrey lost to Florida for the fourth time this year and New York’s offense fizzled in a 6-1 defeat that put the fading Mets on the brink of elimination with two games remaining.

New York fell two games behind NL East-leading Philadelphia, which beat Washington 8-4, and a game back of Milwaukee in the wild-card race. The Brewers topped the Chicago Cubs 5-1.

“We really, really have put ourselves in a tough spot,” Mets manager Jerry Manuel said. “We’re the only ones to blame. We had opportunities and we didn’t get it done.”

Hanley Ramirez had four hits and Josh Willingham homered in his fourth straight game for Florida, which knocked New York out of the playoff race on the final weekend last season.

The Marlins want to do it again, and they haven’t been shy about saying so.

“Obviously, we are not going to play on (Wednesday),” manager Fredi Gonzalez said. “This is as big as it gets for us.”

Santana takes the ball on short rest Saturday after throwing a career-high 125 pitches in his previous start Tuesday against the Cubs. He has never gone only three days between regular-season starts. He did so once for Minnesota in the 2004 AL playoffs, allowing one run in five innings against the New York Yankees.

“It was his choice,” Manuel said. “He came in and begged for tomorrow’s game, regardless.”

The Phillies can clinch their second consecutive division title with a win or a New York loss. Of course, they rallied past the collapsing Mets last year to capture the crown on the final day of the season.

This September hasn’t been much better for the slumping Mets, who are 2-5 since grabbing the NL East lead with a win at Atlanta last Friday.

“It’s been a rough stretch both physically and mentally,” David Wright said. “Nothing else really matters. We’ve got to find a way to win.”

Chris Volstad (6-4) yielded just an unearned run in six innings for Florida. Ramirez scored three times and stole two bases as New York opened the final regular-season series at Shea Stadium with a dud.

Pelfrey (13-11) allowed three runs and eight hits in six innings, falling to 0-4 in five starts against Florida this year. The big right-hander went 0-3 in his final six outings this season, though he pitched well for the most part.

“The difference was their guy made pitches when he had to and I didn’t do that,” Pelfrey said. “No one in here has given up. We still have a chance.”

After Pelfrey was lifted, New York tried four relievers in the seventh. They combined for three walks, a wild pitch and a hit batter as Florida scored twice to make it 5-1.

Bobby Parnell walked pinch-hitter Luis Gonzalez leading off the inning. Pinch-runner Brett Carroll scored when left fielder Daniel Murphy bobbled Ramirez’s single for an error, and Aaron Heilman later walked Willingham with the bases loaded.

Jorge Cantu added a two-out RBI single off Brian Stokes in the eighth.

The Marlins jumped on Pelfrey right away, putting him in a hole after four pitches. Ramirez singled on the first offering of the game, quickly stole second and scored on John Baker’s single. Cantu followed with a double that put runners at second and third, and Dan Uggla had an RBI groundout.

New York had several early chances to respond, but stranded six runners over the first three innings.

The Mets also failed to build on an exciting comeback win Thursday over the Cubs.

“It’s sometimes difficult to figure us out,” Manuel said.

Ryan Church flied out to deep left-center with the bases loaded to end the first. Jose Reyes and Murphy failed to come through with two on in the second. Church grounded into an inning-ending double play with two aboard in the third.

Volstad found a groove after that, allowing only Brian Schneider’s RBI grounder in the sixth. Four Marlins relievers combined for three scoreless innings to finish it.

“I love the atmosphere,” Volstad said. “This is what you play for.”

Willingham hit a solo shot in the sixth, lofting a drive just over the fence in the left-field corner.

Notes: Schneider (back) returned to the lineup at catcher, though he’s not 100 percent. … Ramon Martinez started at second base again. Manuel said he wanted to give Damion Easley (quadriceps) another day to rest. … Tom Seaver, Mike Piazza and Darryl Strawberry received warm ovations when they were introduced before the game as the Mets began saying goodbye to big Shea. They will move next season into a new ballpark, Citi Field. … The Marlins said they will bring back their entire coaching staff and training staff next season. … With 125 runs, Ramirez tied his own team record set last season. … The Mets used eight pitchers, matching a club record for a nine-inning game.

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