Surprise quarter-finalist Sabine Lisicki has attributed her Wimbledon success to the inspiration she has drawn from Lance Armstrong.

The 19-year-old revealed she used the American cyclist's autobiography for extra motivation after knocking out a third seed to set up a last-eight meeting with world number one Dinara Safina.

"It's very inspiring because he never stopped believing that he could beat the cancer and that he could get back on the bike," she said.

Lisicki, one of two unseeded players in the last eight, followed up earlier victories over top-30 ranked Russians Anna Chakvetadze and Svetlana Kuznetsova with a 6-4 6-4 win against ninth seed Caroline Wozniacki, of Denmark.

Lisicki, who did not drop her serve today, has surprised herself by reaching her first grand slam quarter-final but is growing in confidence with every win.

"I've been surprised how far I have got and how well I have started to play," she said. "But I think the key was the very first match where I was actually two points away of losing and I turned it around.

"After that, I really started to play better and better and to believe that I can do good.

"For me it's just one match at a time. I was very happy to have beaten Svetlana. Getting into the second week, I just thought, I have nothing to lose now.

"I'm playing my best tennis so far and I'm very happy and I think I can still get much better. I'm looking forward to the next matches."

Safina came from a set down to beat former champion Amelie Mauresmo 4-6 6-3 6-4 in the first match to be played under the Centre Court roof after rain forced a hold-up midway through the second set.

Italian Francesca Schiavone produced the other shock of the fourth round by beating 26th seed Virginie Razzano, of France, 6-2 7-6.

World number 43 Schiavone, who had not previously gone beyond the third round, will face fourth seed Elena Dementieva after she cruised to a 6-1 6-3 win over fellow Russian Elena Vesnina.

The 27-year-old Dementieva, who reached the semi-finals last year, has yet to drop a set this year and believes she has finally made the adjustment to grass.

"I like to play on grass," she said. "Last year was like a dream come true for me here in Wimbledon. I really enjoyed that experience so it looks like it's really helping me this year as well."

Poland's Agnieszka Radwanska reached the last eight for the second successive year thanks to a straight-sets win against American teenager Melanie Oudin on Court 18.

Radwanska, seeded 11th, broke serve at the end of each set to end the campaign of 17-year-old Oudin, who battled through qualifying and then knocked out sixth seed Jelena Jankovic in the third round.

Eighth seed Victoria Azarenka became the first woman from Belarus to reach the last eight since Natasha Zvereva in 1998 when she defeated Nadia Petrova 7-6 2-6 6-3.

Defending champion Venus Williams remains on course for a final showdown with sister Serena after both gained comfortable successes today.

Venus went through when her opponent, Serbia's Ana Ivanovic, retired injured early in the second set of their Court One clash.

Serena easily disposed of Slovakian Daniela Hantuchova, who was outclassed 6-3 6-1, and will tomorrow face Azarenka, who insisted: "I have nothing to lose.

"She's a great champion here. I will try my best here again. If she's playing good tennis, it's very tough to play against her, especially the serves. It's so tough to play against both Williams sisters."