NEW YORK -- If the Mets want to go to the postseason, they need outfielder Brandon Nimmo to step up for the next month and a half.

Nimmo has stumbled since the All-Star break, entering Friday's action hitting .140 without a home run in the second half, but his fortunes may have changed for the better. After taking Thursday off against the Athletics because of a stomach bug, Nimmo's three-run homer capped a six-run fourth inning as the Mets defeated the Marlins, 7-3, in the series opener at Citi Field.

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New York was down, 2-1, when it rallied to take the lead against Marlins right-hander Roddery Muñoz. Jeff McNeil got the big inning started with a go-ahead two-run homer after Francisco Alvarez drew a one-out walk.

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Muñoz couldn’t record an out after that, allowing another walk and an RBI triple to Francisco Lindor. Miami then brought in right-hander George Soriano, who hit Mark Vientos with a pitch. That brought Nimmo to the plate, and he swung at a first-pitch slider and crushed it to the second deck in right field for his first long ball of the second half and first since July 10 vs. the Nationals.

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It was not the home run that convinced manager Carlos Mendoza that Nimmo was having better at-bats. It was his previous at-bat the inning before even though he struck out. There was more rhythm to Nimmo’s swing and the timing was better, which helped him make better swing decisions.

“He took a swing and I was talking to [hitting coaches Eric Chavez and Jeremy Barnes] and I said, ‘That’s one of the better swings he has taken in the past week or so.’ He goes out there and has that huge homer for us,” Mendoza said.

Nimmo ended up going 2-for-5 with two runs scored and he was glad to contribute to the victory.

“It definitely felt good to help out tonight,” Nimmo said. “That’s all I want to do … is help us win and try to get into the playoffs so we can get our shot and see if we can be that hot team and make our run. We have been working hard. I don’t know -- maybe I have some of those demons out of me with me being sick yesterday. … It felt good to help out tonight.”

Nimmo will not be thinking about what he accomplished Friday during the next game against Miami.

“Nobody cares. We have to go out and win tomorrow, but it’s a good step in the right direction and we’ll keep working,” Nimmo said.

During the slump, Nimmo never stopped working or asked for a day off.

“That says a lot about who he is,” Mendoza said. “When he is not feeling his best and he is going through a rough stretch, he wants to post. He wants to help the team in so many different ways. He has been consistent and he is one of our leaders.”