British number one Johanna Konta's poor run continued as she was beaten by unseeded Ashleigh Barty in the second round of the Wuhan Open in China.
World number seven Konta had the chance to serve for the match but lost 6-0 4-6 7-6 (7-3) to the Australian.
The 26-year-old has lost five of her past seven matches since reaching the Wimbledon semi-finals.
Defending champion Petra Kvitova also fell as she lost her first-round match against Peng Shuai.
The Chinese world number 24 beat 11th seed Kvitova of the Czech Republic 7-6 (9-7) 6-7 (5-7) 7-6 (7-3) in an entertaining encounter.
Konta, who is eighth in the race to qualify for the WTA Finals, received a first-round bye but lost the first seven games against Barty as she struggled for rhythm.
She saw out the second set and served for the match at 5-4 in the third, but a wide forehand smash on break point allowed Barty to force a tie-break.
Barty, ranked 37th in the world, then dominated the tie-break to move into the third round.
"I was unfortunate not to have come through but I think that's also a part of sport and it's part of tennis - you can't be successful and win all the time," Konta said.
"These are the different challenges I'm facing, but in the long run this all makes me a better player and a better competitor."
Earlier, US Open champion Sloane Stephens lost her first-round match in straight sets to world number 55 Wang Qiang.
American Stephens was beaten 6-2 6-2 by Wang of China, just hours after fellow US Open finalist Madison Keys lost to qualifier Varvara Lepchenko.
"It's difficult. It's the end of the year. Even though I played five tournaments, I feel like I have played 25," said Stephens.
Russell Fuller, BBC tennis correspondent
Konta is a player short on confidence, as this fourth consecutive defeat underlined.
She made an abject start to the match, but played with a far greater sense of purpose after rediscovering her potent first serve. And this would have been a fine recovery had she not faltered when serving for the match.
Konta will remain in the eighth and final qualifying position for Singapore unless Svetlana Kuznetsova wins the title.
But if the Russian is unable to make much progress this week, then Konta will still be well placed heading into next week's event in Beijing, one of the big four events on the WTA tour.