NEW YORK -- The New York Mets are losing players almost as fast as they are winning games. The Miami Marlins need to figure out that equation in a hurry.

The surging Mets will look to complete a four-game sweep of the reeling Marlins on Thursday night when the two teams meet at Citi Field.

The wins and the injuries continued piling up for the Mets on Wednesday when Kelly Johnson laced a tiebreaking three-run double in the bottom of the eighth inning to lift New York to a 5-2 win over the Marlins at Citi Field.

Minutes after the game, manager Terry Collins announced that second baseman Neil Walker is expected to undergo season-ending surgery to repair a herniated disk in his back. Five of the Mets' 10 Opening Day starters are out for the season and another three have spent time on the disabled list. Only Curtis Granderson has remained on the 25-man roster all year.

The Mets will get another reminder of their fragility on Thursday, when right-hander Jacob deGrom takes the mound in place of injured Steven Matz. The left-hander was expected to be activated from the disabled list on Thursday but experienced soreness while playing catch on Tuesday.

Yet despite the litany of injuries, the Mets (69-64) have won nine of their last 11 and will enter Thursday just 1 1/2 games behind the St. Louis Cardinals in the race for the second wild card-spot in the National League.

"There's nothing like coming to the ballpark in the big leagues in the month of September in a pennant race," Collins said, his voice rising. "There is nothing like it. The energy level picks up. I'm real proud of the job they've done."

The Marlins (67-66) are plenty banged up as well in the midst of a stretch that threatens to ruin a once-promising season.

Miami capped an 8-18 August in appropriate fashion Wednesday, when right-hander David Phelps, who was supposed to start against the Mets, was instead placed on the disabled list with an oblique injury he suffered while taking batting practice on Tuesday.

In addition, outfielder Marcell Ozuna left in the fourth inning, one inning after he hurt his left wrist while making a diving catch. X-rays were negative and he is day to day.

Phelps became the fifth Marlins player to hit the disabled list in August. Of that quintet, only left-hander A.J. Ramos has returned to the active roster. Miami is missing 40 percent of its rotation with Phelps and left-hander Adam Conley (left middle finger) on the disabled list as well as its two biggest bats. Giancarlo Stanton has been out since Aug. 14 with a left groin strain and Justin Bour hasn't played since July 2 because of a right ankle sprain.

Manager Don Mattingly was in no mood to make excuses Wednesday night, though.

"You look at the whole picture and it's a lot of different things, but we're just not doing enough to win," Mattingly said. "We lost and we weren't very good this month, so it's pretty much on all of us."

Right-hander Jose Urena is scheduled to start for the Marlins against deGrom.

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