Wimbledon, June 28:

No slow start for Venus Williams this time.

After struggling in tight first sets in her opening two matches, the defending champion moved out quickly on Saturday and then raised her game when she needed in the second to beat Spanish qualifier Maria Jose Martinez Sanchez 6-1, 7-5 to reach the fourth round at Wimbledon.

The four-time champion was barely tested in the first set by the 101st-ranked left-hander, but was pushed to the limit in the second when the Spaniard switched to an effective serve-and-volley game that forced Williams to come up with some of her best power tennis.

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, and the American served out the match at love, finishing with her 11th ace of the match. Williams finished with 33 winners, 10 unforced errors and six double faults.

Also advancing to the round of 16 were fifth-seeded Elena Dementieva, who defeated Gisela Dulko of Argentina, 7-6 (2) 7-5, and second-seeded Jelena Jankovic of Serbia who overcame Caroline Wozniacki of Denmark 2-6, 6-4, 6-2.

The tournament has been jolted by a series of early-round upsets that have decimated the seeding lists. Six of the top-10 seeded men were ousted 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.

No 1 Ana Ivanovic’s loss on Friday to 133rd-ranked Zheng Jie of China means two of the top three seeded women are already gone. No 3 Maria Sharapova, the 2004 champion, was bounced out on Thursday by 154th-ranked Alla Kudryavtseva.