American wildcard Frances Tiafoe caused an upset as he eliminated in-form Alexander Zverev at the Western and Southern Open, while top seed Rafael Nadal progressed.
Zverev's 10-match winning streak was ended by Tiafoe, who rallied to triumph in three sets against the fourth seed at the ATP 1000 event in Cincinnati on Wednesday.
Incoming world number one Nadal saw off Richard Gasquet to advance to the round of 16.
Grigor Dimitrov and Juan Martin Del Potro won through to the next round as Adrian Mannarino continued his good form against 15th seed Sam Querrey.
TIAFOE CLAIMS ZVEREV SCALP
All eyes were on Zverev after he upstaged Roger Federer to win the Rogers Cup in Montreal last week - his fifth Tour title of the year.
And many expected the 20-year-old German to continue where he left off, having also claimed the Citi Open.
But the world number seven was clawed back by 19-year-old Tiafoe, who prevailed 4-6 6-3 6-4 for the biggest win of his young career and only his second top-50 victory.
"These are wins that definitely can change your career the right way," Tiafoe said. "This is a big relief for me. We grew up together playing junior grand slams, playing Under-12s, Under-14s. I have known him for forever. Seeing him rise like that, I was, like, 'Maybe I can do the same'. Then he beat me twice, and I was, like, 'All right, maybe I can't'. So me beating him today made me feel pretty good."
NADAL MARCHES ON
It was not his most polished performance, but the 15-time grand slam champion was too good for Gasquet 6-3 6-4.
Nadal closed out the contest, delayed by an hour due to rain, with an ace to improve his head-to-head record to 15-0 against the Frenchman.
Next up for 2013 champion Nadal is Albert Ramos-Vinolas, who shocked 16th seed Gilles Miller 5-7 6-4 6-4.
DEL POTRO TO FACE DIMITROV
Bulgarian seventh seed Dimitrov earned a last-16 meeting with Del Potro thanks to a 7-6 (7-5) 6-4 victory over Feliciano Lopez.
Dimitrov hit 27 winners as Del Potro awaits in the next round.
Playing in Cincinnati for the first time in four years, Del Potro beat American qualifier Mitchell Krueger 6-4 6-4.
MANNARINO STAYS HOT, KYRGIOS ADVANCES
A quarter-finalist at the Rogers Cup, Mannarino trumped Querrey 6-2 7-6 (7-4).
Nick Kyrgios overcame Alexandr Dolgopolov 6-3 7-6 (8-6), while 11th seed Pablo Carreno Busta and veteran David Ferrer were among the other winners.