In brutal conditions – the 95-degree temperatures and stifling humidity had basically wilted Sloane Stephens earlier in the day, and Roger Federer the night before – the 6-foot-6 del Potro managed crucial points and debilitating elements better than his even-taller opponent.
The 11th-seeded Isner was frequently left bent over at the knees, like a staggered boxer.
Del Potro now advances to the semifinals for the second consecutive year.
“I’m so happy to reach another semifinals in my favorite tournament,” said del Potro on court after his win. “It was like an epic match. We both felt tired in the end, we both fight the whole match. I think I survive with my serve in the important moments in the match.”
With the heat rule in effect, the players retreated to the locker rooms for a 10-minute break after the third set. “I lay down on the table, and I didn't want to come back on court again," said del Potro, "because with this heat it’s impossible to play tennis."
“But with this crowd, with these people, it’s too much atmosphere,” del Potro said, explaining how he stayed motivated.
For three sets, Isner surrendered just a single break point. But after the heat-rule respite, del Potro immediately broke the American to open the set and then broke again to finish it, capitalizing on a third break point to claim the match. For his part, the Argentine did not lose serve all afternoon.
WHAT IT MEANS: For these two big men facing off in alpha-dog tennis, one of the main objectives was conserving energy and pouncing on the few break points that were likely to come off their big serves. Del Potro played remarkably clean tennis given the conditions and stakes, notching 49 winners against just 14 unforced errors.
Del Potro, who is ranked a career-high No. 3 (he languished at No. 581 just three years ago), has the possibility to reprise his semifinal of last year – should No. 1 Rafael Nadal beat Dominic Thiem in the second night match. The big Argentine has not been to a Slam final since winning the US Open over Roger Federer in 2009. Del Potro has dropped just one set en route to the semifinals.
John Isner entered the match playing perhaps the best ball of his career over the last six months, as a 33-year-old, newly married and about to become a father. In April Isner won the ATP Masters in Miami, beating No. 3 Cilic, No. 6 del Potro and No. 5 Zverev. And the American also won his 14th tour title this summer in Atlanta. Isner had beaten del Potro two of the last three times they’d met, both on hard courts, but he couldn’t match those heights on Tuesday.
MATCH POINT: If the tennis was largely less than scintillating for much of the afternoon – it was just too hot for that – del Potro’s fan suite, a team of twelve from Tandil, was instrumental in keeping up the energy in Ashe Stadium. Their indefatigable sing-song soccer chants drowned out occasional responses of "USA! USA!," obliterating Isner’s would-be home-court advantage. Del Potro of course has long been an exceedingly popular and sympathetic character in New York, even before the Argentine had his own personal hometown cheering section.