German Alexander Zverev's 10-match winning streak ended with defeat by unseeded American Francis Tiafoe in the second round of the Cincinnati Open.
Zverev, 20, has moved up to seventh in the world rankings following victory over Roger Federer in Montreal.
But he lost 6-4 3-6 4-6 to the 19-year-old Tiafoe, the world number 87.
In the women's event, world number nine Venus Williams was also knocked out in the second round by Australian qualifier Ashleigh Barty.
Barty, ranked 48 in the world, beat the Wimbledon finalist 6-3 2-6 6-2 to earn her first victory over a top-10 player.