Second seed Li Na was beaten 7-6 (7-5) 7-6 (7-5) by Barbora Strycova in the third round at Wimbledon.
China's Li was badly out of sorts against her Czech opponent, who will play 16th seed Caroline Wozniacki next.
Former world number one Wozniacki reached round four with a 6-3 6-0 defeat of Croatia's Ana Konjuh.
Romania's third seed Simona Halep, runner up at this year's French Open, reached round three with a 6-3 4-6 6-4 victory over Ukraine's Lesia Tsurenko.
Halep, 22, will play world number 71 Belinda Bencic next after the Swiss player beat American Victoria Duval 6-4 7-5.
Fourth seed and 2012 runner-up Agnieszka Radwanska trounced Michelle Larcher de Brito 6-2 6-0 and the Pole will play Russia's 22nd seed Ekaterina Makarova, who beat Caroline Garcia 7-5 6-3, in round four.
Petra Kvitova won an epic battle of former champions on Centre Court, the 2011 winner from the Czech Republic seeing off five-time champion Venus Williams 5-7 7-6 (7-2) 7-5.
After the match, Williams looked tearful as she waved farewell to the crowd, but she quashed any talk of retirement.
"There have been people trying to retire me since I was 25," she said. "For some reason, we do that in tennis to our players. It's weird. We don't encourage them to stick around. It's like, 'Get out of here'.
"So I'm not getting out of here. I think this year has been a great year. I've had some tough losses, but I've learned a lot from them. I'm finding my way back on my feet.
"I'm proud of myself for what I'm achieving on the court."
Sixth seed Kvitova will play Shuai Peng in the fourth round after the Chinese woman beat Lauren Davis of the United States 0-6 6-3 6-3.
Australian Open champion Li, 32, has not advanced beyond the third round in eight appearances at Wimbledon and lost in the first round at this year's French Open.
Her match ended in bizarre circumstances when Li, facing match point, successfully challenged a forehand which had been called long, cutting short her opponent's effusive celebrations.
But Li served up a seventh double fault on the replayed point, handing the Strycova, the world number 43, an unexpected victory.
It is the first time the 28-year-old, who served a six-month doping ban in 2013, has reached the fourth round of a Grand Slam tournament.
Wozniacki had lost before the fourth round in her last five major tournaments but the Dane has looked in fine form at Wimbledon this year.
Following her split from former fiance and golfer Rory McIlroy and a first-round defeat at the French Open, Wozniacki took a holiday with Serena Williams and the break appears to have done her good.
"To play good tennis, your head has to be there," said Wozniacki, 23. "I'm in a good place in my head right now. I think that shows on court as well.
"The crowd has been amazing. [But] I'm not a victim. My private life has nothing to do with my tennis.
"When I'm out there, it's a yellow ball, white lines, it's about playing it over the net and inside the lines more than your opponent."
Tenth seed Dominika Cibulkova of Slovakia was beaten 6-4 6-2 by 23rd seed Lucie Safarova, who will play Tereza Smitkova of the Czech Republic next.