Venus Williams of the US returns the ball to Maria Jose Martinez Sanchez of Spain during their match at the Wimbledon tennis championships in London yesterday. --Xinhua/Reuters

Defending champion Venus Williams defeated Spanish qualifier Maria Jose Martinez Sanchez 6-1, 7-5 yesterday to advance to the fourth round at Wimbledon Open.

The four-time winner was barely tested in the first set by the 101st-ranked player. But Williams was pushed to the limit in the second when Martinez Sanchez switched to an effective serve-and-volley game.

"I was very pleased with the performance," the seventh-seeded Williams said. "Things got close in the second set. She was really playing well, and I had to come up with something more than she was giving."

Also advancing to the round of 16 was No. 2-seeded Jelena Jankovic, who rallied after dropping the first set and overcame a knee injury to down 17-year-old Danish player Caroline Wozniacki 2-6, 6-4, 6-2.

Jankovic is the highest-ranked player left in the women's draw after the upsets of No. 1 Ana Ivanovic and No. 3 Maria Sharapova.

In men's play, second-ranked Rafael Nadal charged into the fourth round with a 7-6 (7/3), 6-2, 6-3 win over Nicolas Kiefer.

Nadal, seeking his first Wimbledon trophy, was broken for the first time while serving for the match at 5-1 in the third set. Two games later, the Spaniard held at love to close it out.

Men's winners included No. 8 Richard Gasquet, No. 12 Andy Murray, Janko Tipsarevic, Arnaud Clement, Marin Cilic and Rainer Schuettler, the oldest player left in the draw at 32.

In a five-set marathon that ended in near darkness at 9:30 p.m., Mikhail Youzhny outlasted Radek Stepanek 7-5, 6-7 (5), 6-4, 6-7 (4), 6-3. In the final game, Stepanek tumbled on the slick surface and injured his right wrist. After medical treatment, he resumed playing and Youzhny ended the match quickly.

Williams will next face 18-year-old Russian Alisa Kleybanova, who is into the second week in her Wimbledon debut after defeating Ai Sugiyama 6-4, 6-4.

French Open runnerup Dinara Safina struggled with a thigh injury and lost to Shahar Peer of Israel 7-5, 6-7 (4), 8-6 in a 3 hour, 25-minute match.

Other women advancing to the round of 16 Saturday were fifth-seeded Elena Dementieva, No. 21 Nadia Petrova and 154th-ranked Alla Kudryavtseva, who followed her upset of former champion Marion Sharapova by beating China's Peng Shuai 6-3, 1-6, 6-4.