Britain's Johanna Konta was beaten 6-4 3-6 7-5 by former world number one Venus Williams in the quarter-finals of the Wuhan Open.
Konta, who won 21 of her previous 22 matches and beat world number two Simona Halep on Wednesday, served for a place in the last four in the decider.
However, American Williams, 35, won four games on the trot to set up a semi-final against Roberta Vinci.
Konta's form will see the 24-year-old take over as British number one.
She had started the year 150th in the world but is now 66th and will next week pass compatriot Heather Watson in the rankings.