Brandon Nimmo may have started an uphill climb out of his second-half slump.

The outfielder, who sat out of Thursday’s 7-6 loss to the A’s with an illness, shined for the first time since July with a 2-for-5 night highlighted by a three-run home run in the Mets’ dominant 7-3 win Friday to open the Marlins series at Citi Field.

However, he didn’t hesitate to admit he’s not out of the woods yet.

“No,” Nimmo said after the win when asked if his performance unburdened him. “No, I mean, tomorrow, nobody cares. So we got to go out and try to win tomorrow. But it’s a good step in the right direction and we’ll keep working.”

Nimmo, who said he is still not feeling 100 percent, has struggled since the league’s All-Star break in July and hasn’t looked like the hitter helping the Mets toward a playoff push, as he once did.

During the first half of the season, Nimmo posted an .815 OPS for 16 home runs and 63 RBIs.

Before Friday, the nine-year Met had gone 12-for-86 at the plate with 30 strikeouts and a .444 OPS since the break.

“Yeah, I’ve been very open about it. You know, I’m not doing very well,” Nimmo said of his struggles and discomfort at the plate. “Obviously, the worse you do, the less and less comfortable you feel. But today was a step in the right direction. We’re working every single day to try and get better and be better in the game. We’ll continue to do that.”

Friday night marked his first home run in 27 games — since July 10.

In the bottom of the fourth inning with one out and two runners on, Nimmo contributed to a hot offense that had already scored three runs in the frame off of a two-run homer from Jeff McNeil and a triple from Francisco Lindor.

He blasted the first pitch — an 81.2 mph slider — into the upper right deck (390 feet), knocking in Lindor and Mark Vientos to increase the Mets’ lead to 7-2.

He also started off the night reaching second on a two-base error after Marlins pitcher Roddery Munoz overthrew to first base.

On Friday, manager Carlos Mendoza noticed improved swings from Nimmo, whom he said looked to have better rhythm and timing.

“It’s going to allow him to get into position to make some really good swing decisions because this guy knows the strike zone better than anyone and he can do damage,” Mendoza said. “He had rhythm and he was on time, and the barrel was coming through the hitting zone today. It was different. So that was good to see.”