CHICAGO — Noah Syndergaard reared back and tested the bounds of the radar gun. At one point, he hit triple digits. And though his fastball waned slightly as the night progressed, he had done enough on Tuesday to allay concerns about his prized right arm.

After his fastball suddenly disappeared on July 8 — triggering an 11-day freakout about his health — Syndergaard proved to be fine. It was that reassurance that colored the Mets’ 2-1 win over the Cubs, one made possible by Jeurys Familia’s escape act in the ninth.

The closer allowed the first three batters to reach, loading the bases. But he got Matt Szczur to bounce into a force and induced Kris Bryant to hit into a double play, stunning the fans at Wrigley Field.

Syndergaard allowed only one run — unearned — in 5 2/3 innings. He threw 105 pitches in his first start of the second half. He struck out eight and walked two, a typical ratio in what has been a dominant season.

But it was his batterymate Rene Rivera — the all-glove, no-bat catcher — who delivered the game-winner. Rivera began the night hitting only .190. But with two outs in the ninth, Rivera laced his third hit of the game, a single that drove in Neil Walker with what proved to be the winning run.

The hit made up for Rivera’s throwing error that resulted in the Cubs’ only run.

Familia nailed down his 33rd straight save to begin the season, ensuring that the Mets (50-43) will have a chance to win the series on Wednesday.

Poor judgment led to the Mets falling into a 1-0 hole in the third. Rivera has been Syndergaard’s steady batterymate, mostly because he has a strong enough arm to slow down the running game — one of the righthander’s glaring weaknesses. But Rivera’s arm got the Mets in trouble.

After Willson Contreras doubled to the gap in right-center, Syndergaard threw a wild pitch. Rivera scrambled after ithe ball and made an ill-advised throw to third, hoping to nab Conteras. But the attempt hit the ground well short and well wide of the bag. It sailed into the outfield and Contreras ran home.

Syndergaard did get some help from his defense in the fourth. Cubs starter Jake Arrieta laced a two-out double to right-center and appeared to score when Tommy La Stella followed with a single to right. Umpires initially ruled Arrieta safe, ahead of Michael Conforto’s throw to the plate.

But after a brief review, he was ruled out as Riverao applied a perfect tag on Arrieta’s arm as he reached for the plate.

The Mets tied the score in sixth thanks to Jose Reyes, who flashed his familiar speed to leg out a triple down the rightfield line. Curtis Granderson followed with a fly ball to centerfield that scored Reyes.

But in the seventh, the Mets squandered a chance to inch ahead.

Neil Walker led off with a single, and two batters later, Rivera collected his second hit of the night. With runners on first and second, and the pitcher’s spot due up, Collins had his choice of pinch hitters.

Collins could have gone to Wilmer Flores, perhaps the hottest bat on the bench, though righties typically have had more trouble against Arrieta. Lifetime, Flores is 3-for-13 against the Cubs ace.

Lefty swinging Kelly Johnson was brought back to the Mets for pinch-hitting situations, though his career 0-for-6 against Arrieta may have given the manager pause.

So, Collins settled on perhaps the most maligned player in his dugout, Alejandro De Aza. Historically, he had the edge, 3-for-7 lifetime against Arrieta, including a hit when he faced him earlier this month. But such numbers often mean little, especially when they are amassed over long stretches of time.

More relevant was De Aza’s status as the player seemingly the closest to losing his spot. De Aza struck out to end the inning.

Arrieta delivered his best start in nearly a month. He struck out eight while holding the Mets to only one run in seven innings.