CLEVELAND — If you want a sign of Jarrett Allen’s growth, just go back and watch Monday’s performance. The same young Nets center who used to get dominated by Tristan Thompson utterly wrecked Cleveland’s game plan on both ends of the floor.

Allen had 22 points, on 9 of 10 shooting, and 21 rebounds. He’s the first player to go 20-20 and shoot 90 percent since now-teammate DeAndre Jordan did it in 2016-17. With Jordan sidelined with a sore left ankle, the Nets needed every single play Allen made to gut out a 108-106 win on the second night of a back-to-back.

“For sure it was a little bit of running on fumes. We were all tired from the game before and now we all had to play hard,” Allen said. “The last couple minutes were the hardest part of the game. Just at the end we just had to play with what we’re dealt.”

Allen’s nine offensive rebounds were a career-high, and his 21 boards the second-most he’s ever had. He altered a host of Cleveland shots and blocked two, including Jordan Clarkson’s go-ahead layup attempt with 8.9 seconds remaining.

“Their rim protection was the difference-maker in the game,” Cleveland coach John Beilein said. “We could get to the rim, but we couldn’t finish there all day long.”

Spencer Dinwiddie calls Allen a future All-Star, while ex-teammate Ed Davis predicted he would be a $100 million player someday. While seeing that in print might make owner Joe Tsai wince, it’s not farfetched.

The Nets have already exercised their team option for next season for $3.9 million, and Allen is bound to get a raise after that.

Considering he has piled up the Win Shares in a 2017 draft class that includes Donovan Mitchell, Jayson Tatum and Bam Adebayo — all picked before him at No. 22 — it’ll be a big one. He’s earned it by fixing not only the hole in his game, but shoring up the Achilles’ heel in Brooklyn’s.

The Nets are 28-18 when Allen has managed double-digit rebounds in his career. Seeing that plummet to just 48-75 when he doesn’t should put into perspective just how badly they need him on the glass. That’s essentially the gap between a 50-win contender and a 32-50 lottery team.

Asked whether he’ll be ready to play Wednesday in Boston, Jordan replied, “You have to ask [director of sports science] Dan Meehan.”

The Nets recalled Rodions Kurucs and two-way Timothe Luwawu-Cabarrot from G-League Long Island, but neither played.

The Nets went the entire first half without taking a free throw — the first time they had done that since Nov. 22, 2017, according to Elias Sports Bureau. That was also in Cleveland.