American Venus Williams survived a stiff challenge from Arantxa Sanchez Vicario of Spain yesterday to extend her winning run to 30 matches with a thrilling three-set triumph in the quarter-finals of the tennis tournament.

A powerful forehand into the backhand corner clattered off the Spaniard's racket to complete Williams' 3-6, 6-2, 6-4 victory over Sanchez Vicario, the last player to beat the 20-year-old American.

The win run, which Williams began after a quarter-final defeat to Sanchez Vicario in the French Open, has carried her to the Wimbledon and US Open titles and within two more wins of Olympic gold.

''I didn't have my best day today,'' said Williams, who struggled on serve, committing 13 double faults including four that ended games. ''I had to rely on some experience and some guts.''

Both players had trouble holding serve in the swirling winds but the level of tennis was top notch. Williams, who has one of the best serves in women's tennis, failed to hold serve once in the first set, losing all five service games, three of them finishing on double faults.

She began finding her range in the second set and looked poised to romp to victory in the third before Sanchez Vicario revived.

''Most of the games were pretty close and when I was hitting winners she was still getting some balls back, so I had to keep on going,'' said Williams, who led the third set 4-1 before Sanchez Vicario, one of the great battlers in tennis, made her last charge.

The second-seeded Williams will face fellow-American Monica Seles in the last four. The third-seeded Seles was a 6-0, 6-2 winner against Dominique Van Roost, of Belgium.

The other semi will pit unseeded Australian Jelena Dokic against tenth-seeded Russian Elena Dementieva. Dokic, 17, defeated seventh-seeded South African Amanda Coetzer 6-1,

1-6, 6-1, while the 18-year-old Dementieva overcame twelfth seed Barbara Schett, of Austria,

2-6, 6-2, 6-1.

The 28-year-old Sanchez Vicario, in her fourteenth season on the tennis tour, was at her fighting best against Williams, racing indefatigably from corner to corner to battle the powerful American.

''She served very well at the end,'' acknowledged Sanchez Vicario. ''I gave everything I had. I played my best. Unfortunately, only one can win.''

The Spaniard, who won singles and doubles medals in each of the last two Olympics, was only sorry she would not have a chance at adding to her medals haul.

The men's quarter-final match-ups were completed yesterday as Max Mirnyi, of Belarus, German Tommy Haas, Karim Alami, of Morocco, and Swiss Roger Federer won their third-round matches.