Wimbledon, England -- (Sports Network) - Venus Williams continued her quest for a third straight Wimbledon title with a fourth-round victory over fellow former world No. 1 Ana Ivanovic, while sister Serena was also an easy winner Monday at the All England Club.

Venus, the third seed and a five-time Wimbledon champ, moved into the quarterfinals when a tearful Ivanovic retired in the second set with a thigh injury. The seven-time Grand Slam champion won the first five games of the match and was ahead 6-1, 0-1 when the Serbian star called it quits.

Ivanovic was the top seed here a year ago, and bowed out in the third round.

The former top-ranked Serena, seeded second for this fortnight, needed a mere 56 minutes in a 6-3, 6-1 rout of Slovakia's Daniela Hantuchova.

The Williams sisters have combined for seven of the last nine Wimbledon crowns, with Venus capturing five and Serena two. The two met last year in the championship match, a 7-5, 6-4 victory for Venus. Both of Serena's titles on the famed grass courts of the London suburb came in finals against her sister in 2002 and 2003.

Venus will next take on 11th-seeded Agnieszka Radwanska of Poland. Radwanska eliminated upstart 17-year-old American qualifier Melanie Oudin on Monday with a 6-4, 7-5 win. Oudin previously stunned sixth-seeded Serbian Jelena Jankovic in the third round.

The reigning Australian Open and U.S. Open titlist Serena's quarterfinal opponent will be eighth-seeded Belarusian Victoria Azarenka, who advanced with a 7-6 (7-5), 2-6, 6-3 win over 10th-seeded Russian Nadia Petrova. Azarenka and Serena have split two matches this year, with the American taking a fourth- round tilt on the way to her Aussie Open title and the Belarusian winning the Miami crown in April with a 6-3, 6-1 triumph in the final.

The women's draw lost a fifth top-10 seed on Monday, as big-serving 19-year- old German Sabine Lisicki cooled off No. 9 Dane Caroline Wozniacki 6-4, 6-4. Wozniacki had been 8-0 on grass this season, including a title at Eastbourne two weeks ago.

The rising 18-year-old Wozniacki has appeared in five finals this year, going 2-3.

Fourth-seeded Elena Dementieva breezed to a 6-1, 6-3 victory over fellow Russian Elena Vesnina on Day 7, while another fourth-round result saw Italian veteran Francesca Schiavone take out 26th-seeded Frenchwoman Virginie Razzano 6-2, 7-6 (7-1). The Olympic gold medalist and two-time major runner-up Dementieva will tangle with Schiavone in the quarters.