A month after completing a career Grand Slam and securing the No. 1 ranking, Maria Sharapova failed to get past the fourth round of Wimbledon and lost her grip on the top spot.

The top-seeded Sharapova was outplayed 6-4, 6-3 on Monday by hard-hitting Sabine Lisicki of Germany in windy, rainy conditions on Court 1, ensuring there will be a first-time Grand Slam finalist from the top half of the women's draw.

"She did many things much better than I did today," said Sharapova, who won her first major title here in 2004 at the age of 17. "Of course, I could have done things differently, but not on this particular day."

The 15th-ranked Lisicki recorded her first career victory over Sharapova in four matches, avenging a loss in the semifinals to the Russian here last year.

Lisicki used flat, powerful groundstrokes that neutralized Sharapova, who was trying to become the first woman since Serena Williams in 2002 to win the French Open and Wimbledon in the same year.

"I just missed a couple of points here and there, but overall I just felt very good and confident," Lisicki said.

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Sabine Lisicki celebrates after beating Maria Sharapova at Wimbledon on Monday. (Glyn Kirk/AFP/Getty Images)

Also advancing were four-time women's winner Williams, defending champion Petra Kvitova and second-seeded Victoria Azarenka, but four-time Grand Slam champion Kim Clijsters lost in what she says is her final Wimbledon before retirement later this year.

In men's play, six-time champion Roger Federer was the first to reach the quarters, overcoming an early back problem to beat Xavier Malisse 7-6 (1), 6-1, 4-6, 6-3 and extend his record for most consecutive Grand Slam final-eight appearances to 33.

Federer said his back started hurting in the first few games of the match but he felt much better after taking a medical timeout and receiving treatment.

"Honestly, I'm not too worried," Federer said. "I've had bad backs over the years. I just have to keep an eye on it now ... I hope I'll be 100 per cent on Wednesday."

Djokovic cruises

Top-ranked defending champion Novak Djokovic cruised into the quarters with a 6-3, 6-1, 6-3 win over fellow Serb Viktor Troicki. The entire match was played under the Centre Roof because of rain, which forced the suspension of three men's quarterfinals.

American Mardy Fish led Jo-Wilfried Tsonga 6-4, 1-1; Britain's Andy Murray led Marin Cilic 7-5, 3-1; and Florian Mayer led Richard Gasquet 6-3, 2-1. Two matches never started and will begin Tuesday: American qualifier Brian Baker against Philipp Kohlschreiber, and David Ferrer against Juan Martin del Potro.

Sharapova, who won the French Open four weeks ago for her fourth Grand Slam title, is the biggest name knocked out of the tournament since two-time men's champion Rafael Nadal was upset last week by Lukas Rosol.

Sharapova will lose the No. 1 ranking next week, with either current No. 2 Azarenka or No. 3 Agnieszka Radwanska replacing her, depending on their results the rest of the tournament. Sharapova will fall to No. 2 or No. 3.

"Obviously what I achieved a few weeks ago doesn't just go away in a few minutes," Sharapova said. 'I'll have that for the rest of my career."

After smacking a second-serve 108 mph (174 kph) ace down the middle on her third match point, Lisicki collapsed to her knees on the grass and shook both fists. Among those cheering for Lisicki in the guest box was German NBA star Dirk Nowitzki of the Dallas Mavericks.

"It's just unbelievable," Lisicki said. "For the third time I've beaten the French Open champion here. I'm just so happy. I've lost the three previous meetings against her. Now I just played well and beat her for the first time."

Lisicki will next face fellow German and No. 8 Angelique Kerber, who drubbed Clijsters 6-1, 6-1. Kerber holds a 4-0 career record against Lisicki.

The 47th-ranked Clijsters has said she is retiring after this year's U.S. Open — this time for good, having returned to the sport in 2009 after a two-year break. The Belgian, who has been dogged by injuries this year, walked off Court 3 with a brief wave.

"I didn't really think about that," she said. "I just had the feeling that there was absolutely nothing I could have done today to have won that match."

Azarenka crushes Ivanovic

Azarenka, the Australian Open champion, routed 14th-seeded Ana Ivanovic 6-1, 6-0 in match that was played under the Centre Court roof from 4-1. The match was briefly held up at 4-0 in the second set when Azarenka helped the ball boys pick up pigeon feathers that floated down onto the court from the roof. The Belarusian has dropped only 14 games in her four matches.

Third-seeded Radwanska beat Italian qualifier Camila Giorgi 6-2, 6-3, and will next play No. 17 Maria Kirilenko, who overcame Peng Shuai 6-1, 6-7 (6), 6-3.

Azarenka, Williams and Kvitova are the only women's players left who have reached a Grand Slam final — and they're all in the bottom half of the draw. Sharapova's defeat left four players in the top half who have yet to play for a major championship — Lisicki, Kerber, Radwanska and Kirilenko.

The first player to reach the quarters was 37th-ranked Austrian Tamira Paszek, who beat Italy's Roberta Vinci 6-2, 6-2 to reach the final eight for the second year in a row.

Leading Malisse 4-3 in the opening set, Federer called for a medical timeout and left Centre Court with the trainer for treatment in the locker room. When play resumed eight minutes later, Federer didn't seem visibly affected — although the speed on his first serve lacked its usual velocity.

Still, in the final game, Federer hit two serve winners and closed out the match with a 122 mph (197 kph) ace. He'll next play Mikhail Youzhny, who beat Denis Istomin of Uzbekistan in five sets.

The sixth-seeded Williams won the last three games of the final set to beat 65th-ranked wild card Yaroslava Shvedova of Kazakhstan 6-1, 2-6, 7-5, in cool and gusty conditions on Court 2.

Williams hopped in joy with both feet in the air after hitting a big forehand that forced an error by Shvedova on the first match point, ending a hard-hitting contest that lasted nearly two hours.

"I didn't want to lose today and I thought, 'Just stay relaxed,"' Williams said. "I knew the whole match I could play better."

Williams will next face Kvitova, who rallied from a set and a break down to beat former French Open champion Francesca Schiavone 4-6, 7-5, 6-1 in an error-strewed match on Court 3.

Williams has beaten Kvitova in their two previous matches, including in the 2010 Wimbledon semifinals.

"She's obviously a great grass-court player — as well as I am," Williams said. "I'll be ready."