NEW YORK -- Catcher Jorge Alfaro sure knows how to spoil the party. He hit a pair of home runs -- including his first career grand slam -- to help the Marlins defeat the Mets, 8-4, at Citi Field on Monday night.

With the victory, the Marlins significantly damaged the Mets’ Wild Card hopes. New York is now five games behind the Brewers for the final WC spot in the National League with six games to play in the regular season.

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“[The Mets] are in a little bit of trouble with teams in front of them at this point,” Marlins manager Don Mattingly said. “For us, we just want to continue to play hard. It’s good for us to end the year by playing the Nationals, [the Mets] and the Phillies.

“We are playing teams that are in the hunt. You need to win games, no matter what the situation is. We talk about making sure we are playing hard and doing our part.”

Alfaro started off his big night with a solo shot over the left-field wall -- his 16th homer of the season -- against Mets left-hander Steven Matz in the second inning.

That wouldn’t be all the trouble he dealt to Matz, though. In the sixth, Alfaro knocked the lefty out of the game by hitting the ball out of the yard with the bases loaded, pushing the Marlins’ lead to six.

“I just hit the ball and I was running the bases,” Alfaro said. “That’s how I do it -- run as hard as I can. I realized the ball went out when I saw Starlin Castro running close to me. He was like jogging. I couldn’t believe it. I was trying to put the ball in play, and it went out.”

It was Alfaro’s second two-homer game this season, the last of which came against the Braves on April 6. He now has six career home runs against the Mets in his brief four years in the Majors.

“That was really a big blow,” said Matz. “It wasn’t a terrible pitch, but I just left it up a little bit and he was right on it. It was just really frustrating.”

Manager Don Mattingly noted how a change in Alfaro’s approach at the plate paid dividends Monday.

“Jorge has been pretty good,” the skipper said. “He is making strides. He is not chasing much. He is getting the ball in the strike zone, trying to be more consistent with what he is swinging at. I take that as a positive. He is going to try and keep moving forward with that.”

Even though the Mets answered back with a grand slam of their own in the next half-inning, as Amed Rosario was finally able to get to Marlins left-hander Caleb Smith, it didn’t matter in the end.

Alfaro’s five-RBI night provided enough of a cushion to make the difference for Miami, as they struck first in the four-game series at Citi Field and effectively ended the Mets’ season.