LONDON (AFP) - Top seed and French Open champion Ana Ivanovic was sent crashing out of Wimbledon on Friday by Chinese wildcard Zheng Jie, the world 133.

Ivanovic's 6-1, 6-4 defeat comes just a day after third seed and 2004 champion Maria Sharapova was sent packing by world 154 Alla Kudryavtseva as the chase for the 2008 women's title was thrown wide open.

"It's a real surprise and I have to thank Wimbledon for giving me a wildcard," said the 24-year-old Zheng whose ranking has slipped from a high of 27 because of a serious ankle injury.

"It was tough. Ana has a good serve and a forehand so I tried to play to her backhand. I tried to enjoy it and told myself to keep going," added Zheng, a doubles champion here in 2006.

Zheng goes on to face Hungarian 15th seed Agnes Szavay for a place in the quarter-finals while Ivanovic, who had been lucky to survive in the second round, continues to struggle with her world number one status.

"There was a little bit of pressure being world number one," said 20-year-old Ivanovic.

"But I adjusted and I wasn't as nervous as I was for the first match. It's still a learning experience for me. I tried to find my game but I knew I was struggling. It's been an emotional few weeks and it has taken its toll."

Five-time champion Roger Federer eased into the last 16 only to find Lleyton Hewitt, the 2002 winner, standing in his path to the quarter-finals.

Federer racked up his 62nd consecutive grasscourt win with a comfortable 6-3, 6-3, 6-1 victory over Tunisian-born Frenchman Marc Giquel to keep his dreams of an historic sixth successive Wimbledon title on track.

The Australian 20th seed again shrugged off his hip injury to reach the fourth round for the sixth straight year with a 6-1, 6-3, 7-6 (7/2) win over world number 46 Simone Bolelli of Italy.

"The next round will be difficult. Hewitt's a former world number one. He's won Grand Slam titles. It should be an exciting match," said Federer who hasn't lost on grass since his first round exit here against Mario Ancic six years ago.

Federer leads Hewitt 13-7 in their career meetings.

The Australian has lost the last 11 with his most recent win over the world number one coming five years ago.

Meanwhile, Serena Williams won the battle of former champions when she beat France's Amelie Mauresmo 7-6 (7/5), 6-1.

Williams, the 2002 and 2003 champion, goes on to face Bethanie Mattek for a place in the quarter-finals after her fellow American put out 2007 runner-up Marion Bartoli 6-4, 6-1.

Svetlana Kuznetsova and Anna Chakvetadze helped ease the pain of Russia's Euro 2008 football exit by moving into the last 16.

Fourth seed Kuznetsova celebrated her 23rd birthday with a comfortable 6-2, 6-4 win over Czech qualifier Barbora Zahlavova Strycova and will face Poland's Agnieszka Radwanska.

The 14th seeded Pole put out 16-year-old Russian qualifier Anastasia Pavlyuchenkova 6-3, 6-2.

Chakvetadze, the eighth seed, reached the fourth round for the first time with a 6-4, 6-3 win over compatriot Evgeniya Rodina.

She next faces Czech 18th seed Nicole Vaidisova who put out Australia's world number 43 Casey Dellacqua 6-2, 6-4.

Vaidisova was a quarter-finalist in 2007 where she lost to Ivanovic despite holding three match points and is desperate to put her season back on track after a nightmare run where she lost six successive first round matches.

She stopped the rot with a quarter-final run at Birmingham two weeks ago and even an hour-long rain suspension couldn't disrupt her rhythm on Friday.

Later Friday, Marat Safin, a former world number one, was hoping to follow up his stunning second round win over third seed Novak Djokovic by beating Italy's Andreas Seppi to reach the last 16.