Angelique Kerber suffered her first defeat as world women's tennis number one when Petra Kvitova beat her in three sets in a marathon third-round match at the Wuhan Open in China.
German top seed Kerber saved three set points before a forehand error from Czech Kvitova handed the US Open champion a tense first-set tiebreak.
But Kvitova, showing the battling qualities that have brought her two Wimbledon titles, fought back to force a decider.
Kvitova, seeded 14th, broke Kerber early in the third set to lead 4-2 and despite struggling with cramp, she held her nerve to convert her seventh match point after three hours and 20 minutes on court.
"At the end I think there is no loser. I did everything today. I was fighting until the end," Kerber told reporters.
Kvitova will face Britain's Johanna Konta in the quarter-finals.
Meanwhile men's tennis number one Novak Djokovic has been forced to withdraw from next week's China Open in Beijing because of an elbow injury.
Djokovic, a six-times winner of the tournament who has a 29-0 win-loss record in Beijing, last played in his US Open final loss to Stan Wawrinka this month.
"I am extremely disappointed not to be able to compete at the China Open this year," the Serb said on his website.
"I'm still recovering from my elbow injury and have been advised not to play until my condition improves."
Women's world number two Serena Williams also withdrew from the China Open due to a persistent shoulder injury.