NEW YORK — Juan Martin del Potro’s stay at the U.S. Open really should be over. Nearly was.
The 2009 champion at Flushing Meadows somehow kept staving off defeat in the fourth round against No. 6-seeded Dominic Thiem on Monday. Del Potro was sick and certainly looked sluggish as can be at the outset, dropping the opening two sets with little resistance. Then he trailed by a big margin in the fourth set, even facing two match points.
Still, del Potro never gave in or gave up, eventually working his way all the way back on the strength of powerful serves and thunderous forehands to edge Thiem 1-6, 2-6, 6-1, 7-6 (1), 6-4 over more than 3 1/2 hours and set up a quarterfinal showdown against Roger Federer.
“Thanks so much for all the support you gave,” del Potro told the boisterous Grandstand crowd that regaled the 24th-seeded Argentine with “Ole!” chants. “It helped me a lot. … I won’t forget this match.”
Thiem also aided del Potro by playing his worst tennis when he was closest to victory in the fourth set, which he led 5-2. Thiem served for the match at 5-3, but got broken. Leading 6-5, he managed to get within a point of winning at 15-40 on del Potro’s serve, but a pair of aces at 127 mph and 121 mph erased those two chances. The ensuing tiebreaker was dominated by del Potro, who closed it with a booming cross-court forehand winner on the run.
In the fifth set, del Potro closed things on his second match point, when Thiem double-faulted. How close was this? Thiem actually won more points, 141-139.
When it was over, del Potro raised both arms overhead and threw his head back, enjoying the fans’ adulation, then crossed himself. He joked that he thought he should get a trophy just for winning this one.
It was by far the day’s most enthralling match, with spectators’ roars heard all the way across the grounds at Arthur Ashe Stadium, where Federer was beating No. 33 Philipp Kohlschreiber 6-4, 6-2, 7-5.
The only bit of intrigue came after the second set, when Federer left to take a medical timeout. He said afterward with a laugh that it was so he could get “a bit of a rub on my back — or my bottom — and I didn’t want to do it on court.”
His back had been bothering Federer before the U.S. Open and restricted his practice time, something he blamed for problems while getting pushed to five sets in each of the first two rounds last week. But the lopsided win against Kohlschreiber — who never held a break point — was Federer’s second in a row in straight sets.
Federer improved to 12-0 against Kohlschreiber his record against del Potro is 16-5. But del Potro won their meeting in the 2009 final in New York in five sets for his only Grand Slam title, ending Federer’s streak of five straight U.S. Open championships — and he hasn’t won the trophy since.
The other matchup on that half of the men’s bracket will be No. 1 Rafael Nadal against 19-year-old Andrey Rublev, the youngest quarterfinalist at the U.S. Open since Andy Roddick was 19 in 2001.
Nadal got to the round of eight in New York for the first time since his 2013 title, overwhelming 64th-ranked Alexandr Dolgopolov 6-2, 6-4, 6-1.
“Every victory, every set that you win, is more confidence,” Nadal said. “That what’s I am doing.”
Dolgopolov, who has been interviewed by anti-corruption investigators about a match with unusual betting patterns last month at another tournament, was hesitant to give Nadal too much credit.
“I was just feeling flat,” Dolgopolov said. “I don’t know why.”
Now Nadal gets to play a fifth consecutive unseeded foe in Rublev, who took out No. 9 David Goffin 7-5, 7-6 (5), 6-3.
The top-seeded woman had even less trouble than Nadal did Monday: 2016 runner-up Karolina Pliskova beat 91st-ranked American Jennifer Brady 6-1, 6-0. In the quarterfinals, Pliskova will take on No. 20 CoCo Vandeweghe, who beat Lucie Safarova 6-4, 7-6 (2) to become the third U.S. woman in the next round.
Venus Williams and Sloane Stephens advanced Sunday.
There was a chance for a fourth American to join them, because 15th-seeded Madison Keys was scheduled to play Monday’s last match against No. 4 Elina Svitolina of Ukraine. That winner faces Estonia’s Kaia Kanepi, who beat Daria Kasatkina 6-4, 6-4 to become the first qualifier in 36 years to reach the U.S. Open women’s quarterfinals.
The 32-year-old Estonian is ranked 418th after missing much of the past two years with problems in the soles of both feet and a virus known as a precursor to mononucleosis.
“It’s pretty amazing where I am now,” Kanepi said, “compared to where I was few months ago.”