Defending champion Garbine Muguruza accepted she was not good enough in a defeat to Alison Van Uytvanck after top seed Simona Halep had cruised into the third round at Wimbledon.
Van Uytvanck produced the performance of her career to defeat the third seed 5-7 6-2 6-1 on No.2 Court on Thursday.
Six of the top 10 seeds in the women's draw have bowed out in the first four days, but world number one Halep overcame a shaky start to beat Zheng Saisai 7-5 6-0.
Johanna Konta, a semi-finalist at her home grand slam last year, went down 6-3 6-4 to an impressive Dominika Cibulkova.
Major champions Angelique Kerber and Jelena Ostapenko avoided early exits, while Belinda Bencic saved four match points before fighting back to get past Alison Riske at the All England Club.
'SAD' MUGURUZA LEFT SHELL-SHOCKED
Van Uytvanck had never made it out of the second round at SW19, but she showed aggression and finesse to stun Muguruza.
Muguruza was broken seven times by the inspired 47th-ranked Belgian, ending the Spaniard's hopes of retaining her title.
Two-time major champion Muguruza said: "I think she played big today. She took a lot of risk, and it worked for her. I also think that my level today was not where I wanted it to be. That's also why she could develop that kind of level. It is a little bit sad, but I think she played great."
She added: "I wasn't thinking really I have to defend anything. I was just thinking to go and win it again. I changed a little bit the mindset."
CALM HALEP ENCOURAGED BY FIGHTBACK
Halep was in trouble in the first set, but won 10 games in a row from 5-3 down to set up a third-round encounter with Hsieh Su-wei.
The French Open champion said: "I think there are very good thoughts because I came back after 5-3 down. I started to play much better. I started to calm down and just opening the court better.
"It was not easy. I had pressure a little bit of losing that [first] set, but I didn't panic. I think this was the best thing that I did, I didn't panic. I was just calm, just to play every ball."
KONTA 'NOT LIVING IN THE PAST'
Konta has struggled since reaching the last four and Cibulkova - who missed out on a seeding after Serena Williams was given a discretional promotion - took advantage of the Brit's loss of form.
After the high of her best run at a major on home soil 12 months ago, 22nd seed Konta said: "I don't compare it with a year ago. I'm in a different place with different challenges, basically I'm in a different place.
"I'm appreciating fully how I am working now, how I'm competing now, trying to build on this now. I'm not living in the past."
MAJOR CHAMPIONS MARCH ON, BENCIC HANGS IN THERE
Kerber came through a battle with 18-year-old reigning Wimbledon girls' singles champion Claire Liu, the two-time grand slam winner rallying to triumph 3-6 6-2 6-4.
Ostapenko, winner of the 2017 French Open title, saw off Yulia Putintseva 6-2 6-3, while Daria Gavrilova got past fellow Australian Sam Stosur 6-4 6-1.
Bencic saved four match points in a second-set tie-break before going on to defeat Riske 1-6 7-6 (12-10) 6-2.