Juan Martin del Potro fought off John Isner, 6-7 (7-5), 6-3, 7-6 (7-4), 6-2, on a sweltering day to reach the U.S. Open semifinals. (Andres Kudacki/AP)

They all sit together in a suite, the 10 or so childhood friends Juan Martin del Potro flew in from his small hometown of Tandil, Argentina. They chant the refrain that has grown so popular over the years here, “Ole, ole, ole, ole, Del-poooo, Del-poooo,” and they have coordinated arm motions that they do not have to carve out time to practice because, “They have a lot of time on their hands anyway,” del Potro joked the other night. They don’t have to work hard to rouse the rest of the crowd to follow suit, because the strangers in the less expensive seats love their buddy almost as much as they do.

The boys from Tandil can make anybody playing del Potro feel like a visitor at Arthur Ashe Stadium. Unless, of course, that somebody hails from Greensboro, N.C., and has a chance to become the first American man to reach the U.S. Open semifinals in more than a decade.

Del Potro and John Isner just about split the crowd in the quarterfinals Tuesday for perhaps the first time this fortnight in a match that featured the Argentine. Isner departed with a 6-7 (7-5), 6-3, 7-6 (7-4), 6-2 loss that leaves Andy Roddick as the most recent American man to reach the U.S. Open semifinals back in 2006. The tournament’s favorite son remains.

“Well, I love to play with this energy from the crowd, from the people,” del Potro said before the match. “They make me feel special to play my best tennis every year. I reached another quarterfinals in my favorite tournament, which is something special to me.”

The 6-foot-6 Argentine is on to a semifinal against Rafael Nadal, who survived a 4 hour 49 minute match against Dominic Thiem, winning 0-6, 6-4, 7-5, 6-7 (4-7), 6-7 (7-5) that ended just after 2 a.m. Wednesday.

The defending champion weathered a terrible start in which Thiem, a fellow clay-court maven, took the first set in just 24 minutes. Nadal failed to convert 12 break points, including three at 5-5, 0-40 on Thiem’s serve in the fifth set, but advanced to a Grand Slam semifinal for the third time this year after battling in the tiebreak.

For a man who has only won the tournament once and has skipped it entirely because of injury three times since then, the fervent adoration he meets in New York rivals the crowd’s reverence for five-time champion Roger Federer, who departed late Monday night in a fourth-round upset. That fandom is bolstered by the city’s Latin American population as much as it is by del Potro’s good-guy reputation on tour: Fans often call him “the Gentle Giant.”

Del Potro, 29, feeds off that support and has blown through opponents here — the only set he dropped all tournament was against Isner and his powerful serve Tuesday. Even then, the third-seeded del Potro hit only 14 unforced errors.

“He’s so good, and especially when he gets control of the point. Of course on his forehand side, he doesn’t miss that shot very often, if at all,” Isner, the No. 11 seed, said. “He’s such a tough player and he’s playing well and he likes these conditions. He likes playing on a hard court like this.”

The top-ranked American put up a valiant effort in the suffocating humidity that caused him to lose an estimated eight to 10 pounds and change his shirt 11 times throughout the 3-hour, 31-minute match.

But between the two tall men (Isner is 6-10), del Potro is the better mover and has a more complete game.

Isner, who fell to 4-8 against del Potro, has worked hard this season to improve his returns of serves and stay steadier mentally on court, but he couldn’t break del Potro’s serve to gain the edge he needed. The Argentine instead broke Isner at 30-40 in the fourth set to go up 2-0, and it was all he needed to run away with the match.

Until then, fans had been bracing themselves for another prolonged battle, the likes of which Isner played in the semifinals at Wimbledon against the sport’s other towering giant, 6-8 Kevin Anderson.

Before that match at the All England Club, the farthest Isner had gone in a Grand Slam was the quarterfinals of the U.S. Open in 2011. The second half of the Grand Slam season gave Isner something to be proud of in his 11th year on the ATP Tour.

“[This year] was definitely much better. It’s been a bugaboo of mine for the last six years or so,” Isner said. “It’s definitely something to build on. I’m still trying to build on things and learn from things [from] my experience at Wimbledon and here, two good results for me, back to back. Hopefully I can play like this more in the future and get back to a stage like this more in the future.”

The 33-year-old turns his attention to family now, as his wife, Madison, is due to give birth to the couple’s first child later this month.

Del Potro, on the other hand, keeps his concentration on tennis — if he can focus through the heat, and the noise.

“It’s tricky conditions for the players, for the fans — for my friends who drink beers,” del Potro said with a smile, referring to his suite of childhood companions. “They have dangerous conditions. But they’re having fun.”