When Juan Martin Del Potro had overcome a deficit, the heat and finally American John Isner, he dropped his racket, threw his splayed arms aloft and tossed his head back, eyes closed, doing his best Andy Dufresne imitation.

Considering everything the Argentine star had gone through to get back to playing the best tennis of his life — much less Tuesday’s 6-7 (5), 6-3, 7-6 (4), 6-2 U.S. Open fourth-round comeback — it must’ve seemed like “The Shawshank Redemption.” And it’ll make Friday’s semifinal that much sweeter.

“I’m very happy for my level, for what all has been through to get in this position now,” del Potro said. “It doesn’t matter the final result in the tournament. I just enjoying playing tennis again. I’m enjoying a lot the crowds like this.“I like to play big battles with other guys. That’s makes me feel alive again. After all my problems, I think it’s time to celebrate these kind of things. I love this sport. I love the competition. I’m very proud to be here again.”

Del Potro has much to be proud of. After winning his only Grand Slam title here in Flushing Meadows back in 2009, he had to fight through a string of injuries to both wrists. After his second surgery in 2015, he ended the season ranked 581st and missed nearly a year.

But once del Potro returned, he kept fighting and climbing, climbing and fighting. And a No. 38 ranking in 2016 became No. 11 last year, capped by a semifinal run here. Now after dispatching Isner, he’s back in the semis with either Rafael Nadal or Dominic Thiem standing between him and a final.

“He’s maybe playing some of the best tennis ever right now for him,” said the 6-foot-10, 238-pound Isner, who suffered even more in the 93-degree heat than his foe.

“It’s pretty humid and takes its toll on us players, myself, and I think Juan. … But all in all, he probably handled it a little bit better. It definitely is tough conditions. I wish I could’ve done a little better out there. It just wasn’t to be.”

Isner — trying to become the first American man to reach the semis here since Andy Roddick in 2006 — took the first set in a tiebreaker. But once del Potro rebounded to claim the second, the third-set tiebreaker clearly was the critical moment. And the Argentine won it thanks to a blistering crosscourt forehand.

The American got broken promptly in the fourth then wasted a break point with his 48th unforced error to let del Potro hold and go up 4-1.

Isner had his booming serve and 26 aces but made 52 unforced errors. Del Potro played a clean match with just 14 unforced errors and 49 winners. And despite needing both thighs worked on by a trainer late in the fourth, he broke Isner again to get two wins away from another U.S. Open trophy.

“I have my trophy at home. I like to see that trophy every single day in my home,” del Potro said. “I don’t know if I can get a new one, but I’m doing all my best to try to get [it] again.”

Meanwhile, Isner — who enjoyed a solid year with a Wimbledon semi — will be headed home to await an even more precious arrival, with wife Madison expecting.

“This is going to be life-changing for myself and Maddie and something that we’re very excited about,” Isner said. “I’m going to learn as I go. I’m going to screw up a lot of things at first, and Maddie will probably get mad at me. Now that this tournament is over, my focus is just getting back home and being with her. … [These are] definitely some of the most important days of my life coming up.”