Zverev undone by wonky serve in surprise loss to Schwartzman

Sixth-seeded Alexander Zverev doubled-faulted 17 times on his way out of the U.S. Open. Diego Schwartzman took full advantage in beating him 3-6, 6-2, 6-4, 6-3 to advance to the quarterfinals at Flushing Meadows for the second time.

Zverev's serving problems have dogged him for months and they came back in force against Schwartzman. The lanky German lost his serve eight times, won just 32 percent of second-serve points and amassed 65 unforced errors. He also was hit with a point penalty for swearing in the final set to put Schwartzman up 5-2.

The 20th-seeded Schwartzman, meanwhile, went about his steady baseline and retrieving game, taking the majority of long rallies in a match when some points went on for as many as 35 strokes.

The Argentine, who previously reached the quarterfinals at the French Open last year and Flushing Meadows in 2017, next takes on the winner of the match later between second-seeded Rafael Nadal and No. 22 Marin Cilic.