WIMBLEDON, England (AP)No slow start for Venus Williams this time.

After struggling in tight first sets in her opening two matches, the defending champion moved quickly to defeat Spanish qualifier Maria Jose Martinez Sanchez 6-1, 7-5 Saturday and advance to the fourth round at Wimbledon.

Williams served out the match at love, finishing with a 127-mph delivery the fastest recorded by a woman at Wimbledonfor her 11th ace.

Yeah, 127 is a good way to end it, said Williams, who holds the WTA Tour record at 129 mph.

The four-time champion 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 on Centre Court.

Jankovic appeared to hyperextend her left knee while lunging for a shot in the first set and later took an injury timeout to get her knee heavily wrapped. Jankovic plans to have an MRI before facing Tamarine Tanasugarn in the fourth round on Monday.

Its very sore now, she said. I hope for the best so that I will be able to play my next match.

The 25-year-old Martinez Sanchez had never won a Grand Slam singles match until this tournament and looked out of her depth in the first set against the six-time major winner. But the left-hander scored repeatedly with serve-and-volley winners and angled drop shots and drop volleys in the second set.

It was a great strategy, Williams said. In the first set it wasnt working for her from the baseline. I was impressed with the way she changed strategy and made it really competitive in the second.

The Spaniard rallied from 3-1 down to go ahead 5-4 on serve. But she double-faulted on break point to give Williams a 6-5 lead. Williams finished with 33 winners, as well as 10 unforced errors and six double-faults.

She had played erratically in her first two matches against modest British opponents on Centre Court, winning the first set in a tiebreaker against Naomi Cavaday and pressed to 7-5 in the first set against Anne Keothavong.

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.

Jankovic is the highest-ranked player left in the womens draw after the upsets of No. 1 Ana Ivanovic and No. 3 Maria Sharapova. For a while Saturday, she looked in danger of joining them to make it the first time in the Open era that the top three seeded women failed to make the fourth round at a Grand Slam.

I was thinking maybe Im the next one, Jankovic said.

Jankovic limped through the third set, but still dropped only two games to close out the match as Wozniacki committed unforced errors on key points. Jankovic complained that the leg wrap was too tight and had the trainer remove it after the fifth game.

Russia's Dinara Safina reacts
AP - Jun 28, 2:05 pm EDT

The physio said I probably strained it, Jankovic said. She taped it but I couldnt move itIm not used to it. I took a risk to play without the tape, which the physio was not happy about, but I had to do what I had to do.

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. Safina was up a break in the final set but, after receiving treatment, lost the lead and failed to serve out for the match. She was in tears during the final game and could only serve at half speed.

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 Chinas Peng Shuai 6-3, 1-6, 6-4.

Mens winners included No. 8 Richard Gasquet, No. 12 Andy Murray, Janko Tipsarevic, Arnaud Clement and Rainer Schuettler, the oldest player left in the draw at 32. Murray, carrying Britains perennial hopes for a first homegrown male champion since 1936, had 15 aces in a 6-4, 6-7 (4), 6-3, 6-2 win over Tommy Haas.

The tournament has been jolted by a series of early upsets that have decimated the seeding lists.

Six of the top-10 seeded men have been knocked out so far before the fourth round: No. 3 Novak Djokovic, No. 4 Nikolay Davydenko, No. 5 Ferrer, No. 6 Andy Roddick, No. 7 David Nalbandian and No. 9 James Blake.

Nadal, who lost to Federer in the last two finals, was paired against Nicolas Kiefer.

Roger Federers next opponent is 2002 champion Lleyton Hewittthe last man to win the title before the Swiss star began his run of five straight championships.