LONDON -- Add Serena Williams to the list of big names eliminated early at this wild and unpredictable Wimbledon.
The defending champion failed to close out a seesaw third set Monday, dropping the last four games against Sabine Lisicki of Germany to lose 6-2, 1-6, 6-4 in the fourth round and end her career-best 34-match winning streak.
"I'm still shaking," Lisicki said in a postmatch interview, covering her face with her hands to wipe away tears. "I'm just so happy."
It was the latest in a string of upsets that has jolted the tournament, with defending champion Roger Federer and Rafael Nadal knocked out in the first three days -- along with Maria Sharapova's loss and Victoria Azarenka's withdrawal on the women's side.
Sloane Stephens of the U.S. reached her second Grand Slam quarterfinal of the year, beating 19-year-old Monica Puig of Puerto Rico 4-6, 7-5, 6-1.
The 17th-seeded Stephens is the last American singles player left at the grass-court tournament.
"I probably couldn't be more disappointed," Williams said. "I think I may have backed off of a success. I was playing something successful. I didn't continue that path. The result didn't go the way it could have gone had I continued to play the way I did in the second set."
After dropping the first set, Williams looked to be cruising, winning nine straight games to take a 3-0 lead in the third. The players then traded breaks to give Williams a 4-2 lead, but the American couldn't win another game despite having four break points at 4-3.
Those would have given her a chance to serve for the match. Instead, Lisicki held, broke again, and converted her second match point with a forehand winner.
Williams said her serve -- usually her main weapon -- let her down in the third set.
"I felt that I was on the verge of winning," she said. "At that point I just was physically unable to hold serve. ... You have to be ready and willing to hold your serve. I wasn't willing or able, probably didn't even want to hold my serve today."
Lisicki reached the semifinals at the All England Club in 2011, but this will rank as her biggest victory at the grass-court Grand Slam. She has now eliminated the reigning French Open champion the last four times she has played Wimbledon, having missed the tournament in 2010. She ousted Sharapova in the fourth round last year.
Britain's Laura Robson also lost. She couldn't recover from her missed chances in the first set and fell 7-6 (5), 7-5 to Kaia Kanepi of Estonia, failing to become the first British woman in the quarters of any Grand Slam since 1984. Kanepi will face Lisicki in the quarterfinals.
Former champion Petra Kvitova also reached the quarterfinals, beating Carla Suarez-Navarro of Spain 7-6 (5), 6-3.
She was joined minutes later by Kirsten Flipkens of Belgium, who reached her first career Grand Slam quarterfinal by ousting Flavia Pennetta of Italy 7-6 (2), 6-3 -- a year after her ranking plummeted as low as 262nd because of injuries.
Kvitova served for the first set at 6-5 but was broken at love and then lost four straight points in the tiebreaker to trail 4-3. But she capitalized on a couple of errors by the Spaniard and converted her first set point when Suarez Navarro netted a backhand.
In the second, she broke to lead 4-2, and served out the match at love when Suarez Navarro sent a forehand long.
The 18th-ranked Suarez Navarro was the first Spanish woman since 2001 to reach the fourth round at the All England Club.
Kvitova will next play Flipkens, whose career-best Grand Slam showing comes after she had much of 2012 ruined by injuries, including blood clots in her calf. She missed last year's Wimbledon but has bounced back this year and is currently ranked 20th.
After clinching the win against Pennetta with an overhead smash, Flipkens fell on her back on the grass, covering her face with her hands in apparent disbelief.
Former French Open champion Li Na won a matchup of 30-somethings to reach the quarterfinals for the third time, routing Roberta Vinci of Italy 6-2, 6-0.
The 31-year-old Chinese player broke the 30-year-old Vinci six times to wrap up the win in just 55 minutes on Court 3.
The 11th-seeded Vinci was trying to reach her first Wimbledon quarterfinal, having also reached the fourth round last year.
The sixth-seeded Li will next play No. 4 Agnieszka Radwanska of Poland, who beat Tsvetana Pironkova of Bulgaria.
Information from The Associated Press was used in this report.