TENNIS: Americans Andy Roddick and Venus Williams joined already-beaten men's top seed Roger Federer in the favourites' exodus from the Olympic tennis tournament yesterday.

Men's second seed Roddick and Williams, the 2000 Olympic women's singles and doubles champion, both lost in third-round upsets a day after Swiss world number one Federer was beaten by a Czech teenager in the second round.

Williams' 6-4 6-4 defeat by France's Mary Pierce on court one meant the Americans have no representatives in the quarter-finals of the women's singles after Chanda Rubin and Lisa Raymond also lost in the third round yesterday.

"Obviously I would have liked to have done better. I just have to learn from my mistakes," said a jaded-looking Williams.

Forty-seven-year-old Martina Navratilova, is now shouldering the US women's medal hopes with Raymond in the doubles.

US Open champion Roddick lost 6-4 6-4 to Chilean Fernando Gonzalez on centre court.

Like Federer, who lost in three sets to Czech Tomas Berdych on Tuesday, the American looked surprisingly out of sorts on the fast, blue hardcourt and Gonzalez fully deserved one his finest career victories.

Gonzalez plays either French eighth seed Sebastien Grosjean or Spain's Feliciano Lopez in the quarter-finals.

He and team-mate Nicolas Massu, the 10th seed who is also through to the third round, are seeking to become Chile's first Olympic gold medallist.

Roddick, already knocked out of the doubles, will now prepare for the defence of his US Open title which starts on August 30th. Spain's Carlos Moya, the third seed, is now the favourite for the men's gold.

The exit of Williams, seeded sixth, was a boost to the hopes of Belgian top seed Justine Henin-Hardenne and number two Amelie Mauresmo of France, who thrashed Chanda Rubin 6-3 6-1 yesterday.

Henin-Hardenne needed only 45 minutes to defeat Australia's Nicole Pratt 6-1 6-0 on centre court and she will next play Pierce.

Mauresmo faces 19-year-old fifth seed Svetlana Kuznetsova in the last eight after the Russian brushed aside Swiss 10th seed Patty Schnyder 6-3 6-3.