Alize Cornet of France reacts after defeating Serena Williams of the US in their women's singles tennis match at the Wimbledon Tennis Championships, in London June 28, 2014. [Photo/Agencies]

"She helped me a little bit," Cornet said.

Two particular strokes troubled Williams: Her serve let her down repeatedly, with a total of seven double-faults and five breaks; her backhand produced 12 unforced errors.

In the third set, Cornet led 5-2 but was broken serving for the match. On her second chance, she steadied herself, delivering a perfect drop shot on match point.

When Williams netted the response, Cornet pounded her chest with her fist. Then she hopped around Court 1, before kneeling to kiss the grass.

Cornet had been 0-13 against top-20 opponents in Grand Slam matches.

"I don't really know what I did wrong," said Williams, whose sister Venus lost Friday. "Usually I do. Usually I know I did this, this, and that."

It was by far the most significant - and surprising - outcome on a wet day full of starts and stops.

Three other past Wimbledon champions won on Center Court, where the roof was closed and soccer star David Beckham was in the Royal Box: Rafael Nadal, Roger Federer and Maria Sharapova.

For his third match in a row this year at Wimbledon, two-time champion Nadal dropped the first set before coming back to win, this time beating 63rd-ranked Mikhail Kukushkin of Kazakhstan 6-7 (4), 6-1, 6-1, 6-1.

"From the very first points of the second set, he improved a lot. All his shots just started to be much more hard, powerful and more aggressive," Kukushkin said. "It was like a different player."

Sharapova, the 2004 champion, was up next in the main stadium, and she, too, overcame a slow start. But after falling behind 3-1, she won 11 consecutive games for a 6-3, 6-0 victory over 44th-ranked Alison Riske of the United States.

As for Federer, who has collected seven of his 17 major trophies at the All-England Club, there really was never any trouble spot. He needed less than 75 minutes to eliminate 35th-ranked Santiago Giraldo of Colombia 6-3, 6-1, 6-3 and hasn't lost a set through three matches.

Nadal next faces 19-year-old Australian Nick Kyrgios; Federer meets No 23 Tommy Robredo of Spain, who beat 2013 semifinalist Jerzy Janowicz of Poland 6-2, 6-4, 6-7 (5), 4-6, 6-3; and No 8 Milos Raonic, only the second Canadian man in the Open era to get to Wimbledon's fourth round, plays either No 10 Kei Nishikori of Japan or unseeded Simone Bolelli of Italy, whose match was suspended because of darkness at 3-all in the fifth set.

In the women's fourth round, Sharapova faces No 9 Angelique Kerber. Cornet, meanwhile, takes on No 13 Eugenie Bouchard, a 20-year-old Canadian who was a semifinalist at the year's first two majors.

"It shows all of you who asked me if I'm ready to play Serena in Round 4," Bouchard said. "That's one of the reasons I don't look far ahead."