Del Potro rallies to face Federer in quarterfinal

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.