NEW YORK -- The biggest win of the season for the New York Mets was about 15 minutes old when the black cloud perpetually hanging above the team opened up yet again.

The Mets crept closer in the National League wild card race Wednesday night, but a dramatic 5-2 win over the Miami Marlins was overshadowed when manager Terry Collins ended his post-game press conference by announcing second baseman Neil Walker will undergo season-ending surgery to repair a herniated disk in his back.

Walker, who has missed the last four games, is expected to speak to reporters Thursday. He is hitting .282 with 23 homers and 55 RBIs, all numbers that rank second on the Mets among players who have spent the entire season with the team.

"We're certainly very disappointed that it's come to this," Collins said. "He's had a tremendous year for us."

Collins' bombshell -- he volunteered the information after a spokesman gave the "Thanks Terry" indicator that the press conference was over -- capped a day of mixed signals from the Mets regarding Walker's condition.

General manager Sandy Alderson said Wednesday afternoon that Walker's ailment was routine and that "based on the information we have currently, Neil can play."

Hours later, though, Collins said Walker was experiencing numbness in his leg and foot and that surgery was an option. Even if Walker were to return, Collins said, he would be unlikely to play more than three or four games in a row.

Kelly Johnson, who started at second base Wednesday and delivered the tie-breaking, three-run double with two outs in the bottom of the eighth, said Mets players were not shocked to learn the Walker news.

"We probably knew a little more than most, just because we have those conversations," Johnson said. "Whatever happens, we're with him 100 percent."

Walker is the Mets' fifth Opening Day starter to suffer a season-ending injury. Of the 10 players who took the field for New York against the Kansas City Royals on Apr. 3, only Curtis Granderson has remained on the active roster all season.

Johnson and Wilmer Flores, who hit a two-run homer in the second, are the two players most likely to fill in for Walker. Flores started at first base Wednesday but has made 56 career starts at second base.

"We have a good bench," Flores said. "Everybody that has the opportunity to go out there has done the job. We deal with what we've got. We'll keep battling."

The reigning National League champion Mets (69-64) have won the first three games of a four-game series against the Marlins and nine of their last 11 overall to move within 1 1/2 games of the St. Louis Cardinals in the race for the National League's second wild card.

"All the injuries, all the different things that have happened, they've hung in there," Collins said. "Heading into this last month, we're in a race."

Addison Reed (4-2) earned the win with a perfect eighth inning while Jeurys Familia earned his team-record 44th save with a 1-2-3 ninth. Starter Bartolo Colon allowed two runs (one earned) on seven hits and no walks while striking out three over seven innings.

Christian Yelich had two hits, including a homer leading off the sixth, while J.T. Realmuto had three hits for the Marlins (67-66), who have scored just eight runs during a five-game losing streak.

The Marlins, who are without middle-of-the-order hitters Giancarlo Stanton and Justin Bour, began the month with a one-game lead in the race for the second wild card but went 8-18 in August to fall 3 1/2 games behind the Cardinals.

"We haven't been playing well enough to win in general," Marlins manager Don Mattingly said. "We have lost some guys, but we've talked about it before: A lot of teams have lost guys, so if it has affected or not affected (them), you're still not going to sit here and talk about it."

Marlins right-hander Jake Esch, who was recalled from Triple-A New Orleans to make his major league debut after scheduled starter David Phelps suffered an oblique injury while taking batting practice Tuesday, allowed two runs on seven hits and three walks while striking out two in 4 1/3 innings in his major league debut.

"This is a big game for the Fish and unfortunately we couldn't pull it out," Esch said. "But hey, there's nothing like getting thrown in the fire."

NOTES: After the game, the Mets acquired RHP Fernando Salas from the Los Angeles Angels of Anaheim in exchange for Single-A RHP Erik Manoah. To make room for Salas on the 40-man roster, the Mets transferred OF Justin Ruggiano (shoulder) to the 60-day disabled list. … Marlins CF Marcell Ozuna left after the fourth inning due to a sore left wrist suffered when he made a diving catch in the third inning. … While Marlins RHP Jake Esch made his big league debut, Mets RHP Bartolo Colon made his 494th career start, breaking a tie with Mark Buehrle for 50th place all-time.