LONDON – Maria Sharapova's hopes of winning a second Wimbledon title were shattered Monday as the world No. 1 was comprehensively beaten 6-4, 6-3 by Germany's Sabine Lisicki in the fourth round. The world No. 15 had top seed Sharapova on the back foot early in the first set, forcing her into a string of uncharacteristic errors, and did not let up until she had gained revenge for her semifinal defeat by the Russian last year. Lisicki, who had complained about her second-round opponent Bojana Jovanovski's grunting, was forced to endure Sharapova's loud wails, but kept her concentration to break the French Open champion decisively in the 10th game of the first set. She broke again early in the second and closed it out, converting her third match point with an ace. “It is just unbelievable for me, I'm just so happy,” Lisicki said after falling to her knees with both fists clenched in celebration. In the quarterfinals, the German will play her compatriot Angelique Kerber who ended the run of Belgian Kim Clijsters 6-1, 6-1 . Six-time Wimbledon champion Roger Federer shrugged off a rare medical time-out to defeat Xavier Malisse 7-6 (7/1), 6-1, 4-6, 6-3 to reach a 33rd successive Grand Slam quarterfinal. The Swiss great goes on to face either Russian 26th seed Mikhail Youzhny or Denis Istomin of Uzbekistan for a place in the semifinals. Clijsters, who had already announced she will retire for good after the US Open, saw her ninth and last All England Club campaign end in bitter disappointment out on Court Three. The 29-year-old former world No. 1 triumphed at the US Open in 2005, 2009 and 2010, as well as at the 2011 Australian Open, but Wimbledon always presented its own particular problems. She never improved on her semifinal runs in 2003 and 2006. Four-time champion Serena Williams dug deep to book a place in the quarterfinals, seeing off ‘golden-set' challenger Yaroslava Shvedova 6-1, 2-6, 7-5 just in time before the rain came back down at a gloomy All England Club. Kazakhstan's Shvedova, who became the first player to win a set at a grand slam without dropping a point in the previous round, troubled the American as the dark clouds gathered above Court Two but was undone by a late flurry of pace and power. “I felt fine out there I think we both wanted to keep playing because it was so deep into the match,” Williams said. “I'm not tired so I feel good. I feel like I can play so much better than what I have been playing.” Williams, 30, and 13-times grand slam champion, will next face holder Petra Kvitova who overcame an error-filled performance to rally from a set and a break down and outlast Francesca Schiavone 4-6, 7-5, 6-1n. In a matchup of two former Grand Slam winners, Kvitova wasted 10 break points in the first set. She finally broke back for 2-2 in the second when Schiavone double-faulted. However, the fourth-seeded Czech took charge by jumping out to a 5-0 lead in the third set and served out the match at love. Schiavone, the 2010 French Open winner, won the first set despite hitting just two winners and making 16 unforced errors. Kvitova then won the second despite having four winners and 14 unforced errors. Polish third seed Agnieszka Radwanska reached the quarterfinals with a 6-2, 6-3 win over Italian qualifier Camila Giorgi. Radwanska will face either Russian 17th seed Maria Kirilenko or Peng Shuai of China for a place in the semifinals. In another last 16 match, Tamira Paszek of Austria beat Roberta Vinci of Italy 6-2, 6-2. — Agencies