Newly crowned French Open champion Li was humbled in the second round by German wildcard Sabine Lisicki, losing 3-6, 6-4, 8-6 after squandering two match points in the decisive set.
The Chinese third seed, whose success at Roland Garros earlier this month has been hailed as a milestone for Asian tennis, struggled to cope with the power of her big-hitting 21-year-old rival.
Lisicki, who collapsed in tears on Centre Court after clinching the win, reeled off 17 aces and several serves that topped 120 miles per hour (190kph) throughout the match, leaving Li powerless to respond.
"From the first point until the end of the match, every serve was like 117mph. It's impossible for women," Li said afterwards.
Lisicki, whose career suffered a huge setback in 2010 when a serious ankle injury sidelined her for four months, will tackle Japanese qualifier Misaki Doi for a place in the last 16.
"I always had a very good serve and it's one of the best in women's tennis I think," Lisicki said. "It's very good to have a weapon like that."
Li's exit was the only major upset on a fourth day where wet weather again caused headaches for schedulers.
Williams meanwhile booked her place in the third round after coming from behind to defeat Romanian teenager Simona Halep 3-6, 6-2, 6-1.
But Williams appeared to accuse tournament organisers of sexism after being unimpressed with the decision to schedule her match on Court Two.
She insisted that reigning men's champion Rafael Nadal and second seed Novak Djokovic - who have won fewer Wimbledon titles between them than her - would never be moved away from Centre Court or Court One.
"They like to put us on Court Two, me and Venus, for whatever reason. I haven't figured it out yet. Maybe one day we'll figure it out," said Serena.
"They (Nadal and Djokovic) are never moved across. Actually, Venus and I have won more Wimbledons together than a lot of the players or by ourselves in doubles even.
"I don't make it a big issue, but I think at some point maybe I should."
The rain delays meant several of the women's second round matches will now be played on Friday, including top seed Caroline Wozniacki's match against Virginie Razzano and fifth seed Maria Sharapova's tie with Briton Laura Robson.
In the men's draw, Djokovic cruised into the third round as former champion Lleyton Hewitt was denied an upset in a thrilling five-set duel with fifth seed Robin Soderling.
Serbian second seed Djokovic - who has lost only one match all year - maintained his red-hot form with a ruthless straight sets dismissal of South Africa's Kevin Anderson, winning 6-3, 6-4, 6-2 in just under two hours.
"I served well, I played well, I returned really well. That was the key," said Djokovic, who faces Cypriot number 32 seed Marcos Baghdatis in the third round.
While Djokovic blasted his way into the last 64, Sweden's Soderling was given a punishing examination by Hewitt on Centre Court before finally prevailing 6-7 (5-7), 3-6, 7-5, 6-4, 6-4.
Soderling now faces either Australian youngster Bernard Tomic or Russia's Igor Andreev in the next round.
The shock result of the day saw Lu Yen-Hsun down Serbian 13th seed Viktor Troicki.
Lu, a quarter-finalist in 2010, won 7-6 (7-5), 6-4, 6-4 and will face French 15th seed Michael Llodra of France for a place in the last 16.
Another John Isner marathon briefly looked possible at Wimbledon before the towering American was bundled out in the second round by Spain's Nicolas Almagro in four sets.
Isner returned to Court 18, which now boasts a plaque to commemorate last year's record-shattering 11-hour epic win against Nicolas Mahut, but was beaten 7-6, 7-6, 6-7, 6-3.
Isner had beaten Mahut in a much-hyped rematch in the first round but was never able to make much impression against the hard-hitting 16th seed Almagro.
- AFP/ReutersTags: sport, tennis, united-kingdom First posted June 24, 2011 06:41:00