ATHENS, Aug 18: France's Mary Pierce knocked defending Olympic champion Venus Williams out of the singles on Wednesday with a 6-4 6-4 upset victory in the third round.

Sixth seed Williams, already out of the doubles which she also won four years ago in Sydney with sister Serena, had no answer to her unseeded but revitalised French opponent on court one.

Williams's shock defeat meant the United States had no players left in the women's singles after team mates Lisa Raymond and Chanda Rubin also lost on Wednesday. Men's second seed Andy Roddick also exited on a dire day for the Americans.

Pierce, the 29-year-old 2000 French Open champion, will play either Belgian top seed Justine Henin-Hardenne or Australian Nicole Pratt in the quarter-finals. Earlier on Tuesday, US Open champion and world No 2 Andy Roddick of the United States went out of the Olympic tennis tournament here Wednesday when he lost to 16th seed Fernando Gonzalez of Chile in straight sets.

Roddick, the highest-ranked player after Australian Open and Wimbledon champion Roger Federer's defeat on Tuesday, lost 4-6, 4-6 in 1hr 12min. Gonzalez, the world No 20, who had beaten Roddick once in three previous encounters in Cincinnatti two years ago, now plays eighth seed Sebastien Grosjean of France or Feliciano Lopez of Spain in the quarter-finals.

Gonzalez, 24, broke him in the third to take the first set in 34min and in the ninth game to serve out the match in another 38 minutes. -Reuters