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CHICAGO — Nolan McLean’s presence on the mound Thursday night was the Mets’ best predictor of success, but they were going to need more than their de facto ace to preserve their lead for the NL’s final wild card.

The Mets got all of it: Big swings. Defense. And a giant boost from a bullpen that has been pushed to the limit this week.

Already knowing the Reds had won and would assume position for the third and final wild card if they didn’t seize this series rubber game against the Cubs, the Mets pounced early and held on for an 8-5 victory at Wrigley Field.

It left the Mets with a one-game lead on the Reds and ahead of the Diamondbacks (who lost to the Dodgers) by two games.

The Mets do not hold the tiebreaker against either Cincinnati or Arizona, making it imperative they finish at least one game ahead.

It’s down to the final weekend, with the Mets opening a series in Miami. The Reds play in Milwaukee. The D’backs play in San Diego.

One will emerge with a ticket to face the Dodgers in next week’s wild-card round.

Brett Baty brought the thunder with a three-run homer, and Francisco Lindor also went deep on a night the Mets received a combined 3 2/3 innings of scoreless relief from Ryne Stanek, Brooks Raley, Tyler Rogers and Edwin Diaz.

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McLean stormed into the sixth with a 6-1 lead, but never escaped the inning. He struck out a career-high 11, and also was tagged for the most earned runs (five) in any of his eight starts since his promotion from Syracuse.

Over 5 1/3 innings, he surrendered five hits and two walks as his ERA jumped from 1.27 to 2.06.

The Mets gave McLean a two-run lead before he even threw his first pitch. Pete Alonso’s double put runners on second and third — Lindor led off with a walk — and Mark Vientos hit a pop-up, on which Dansby Swanson fell into the third-base grandstand as he caught it.

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Lindor was awarded home plate as a result of Swanson falling into the stands.

Brandon Nimmo’s ensuing RBI single gave the Mets a 2-0 lead. Lindor homered in the third to extend that lead to 3-0. The blast gave the Mets three players — Juan Soto and Alonso are the others — with at least 30 homers in a season for the first time in franchise history.

Lindor and Soto also became the third pair of teammates in MLB history (joining Darryl Strawberry and Howard Johnson with the 1987 Mets and Ellis Burks and Dante Bichette with the 1996 Rockies) in the 30/30 club for homers and stolen bases.

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Baty gave the Mets plenty of cushion with a three-run in the fourth that buried the Cubs in a 6-0 hole. Nimmo and Luis Torrens each singled before Baty went to the opposite field and cleared the ivy in left against left-hander Shota Imanaga.

The homer was Baty’s 18th this season.

McLean dented in the fourth, when Seiya Suzuki homered with two outs to slice the Mets’ lead to 6-1.

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Dansby Swanson blasted a homer in the fifth to give the Cubs their second run.

Entering the day McLean had allowed only one homer in his first seven major league starts. McLean’s inning began with a strikeout of Pete Crow-Armstrong. The strikeout was McLean’s ninth of the night, a new career high.

Before the inning concluded he struck out Matt Shaw for No. 10. Tyrone Taylor stroked a two-run double in the sixth that knocked out Imanaga and buried the Cubs in an 8-2 hole.

Nimmo and Baty each singled ahead of Taylor, who returned from the injured list a night earlier to claim a share of the starting center field job.

Suzuki’s second homer of the game, a three-blast in the sixth, pulled the Cubs within 8-5 and removed McLean, whose struggles began with one out: Ian Happ walked and Moises Ballesteros doubled him to third. Suzuki clobbered an 0-1 pitch into the left-field seats.

Stanek replaced McLean and recorded the final two outs in the inning.