German veteran Philipp Kohlschreiber got the better of sensational young compatriot Alexander Zverev Saturday, sending the fourth-seed crashing out of the US Open 6-7 (1/7), 6-4, 6-1, 6-3.
Zverev, 21, leads the ATP tour with 45 match wins this season, lifting titles in Munich, Madrid and Washington and reaching finals in Miami and Rome.
But it was 34-year-old Kohlschreiber moving into the round of 16, where he'll face either 13th-seeded Diego Schwartzman of Argentina or Japanese 21st seed Kei Nishikori, the runner-up in 2014.
"I think it was a really entertaining match," said Kohlschreiber, who is in the last 16 at Flushing Meadows for a fifth time.
"You have Sascha with the big serve, big strokes. My variety of the game worked out perfectly."
Zverev led 3-0 in the fourth set but lost the last six games.
"I returned very well," Kohlschreiber said. "He usually likes to have free points on his serve, that was a key factor today that I played a lot of force back on his service games."
"Slice, angles, they all paid off," Kohlschreiber said. "Lucky me today."