American Andy Roddick's [ Images ] hopes of Olympic [ Images ] gold disappeared on Wednesday when he lost 6-4, 6-4 to Fernando Gonzalez [ Images ] of Chile in a third round upset in the men's singles.

Gonzalez outplayed the second seed, who was the hot favourite for gold following the shock defeat of Swiss world number one Roger Federer [ Images ] in the second round on Tuesday.

The Chilean 16th seed quickly broke Roddick's usually fearsome serve on centre court to take the first set and broke again for 5-4 in second before holding his nerve to seal a superb victory.

Gonzalez plays either French eighth seed Sebastien Grosjean or Spain's Feliciano Lopez [ Images ] in the quarter-finals. Roddick, already knocked out of the doubles, will now prepare for the defence of his U.S. Open title after the Games.