Spain's third seed Carlos Moya became the latest casualty in the men's singles tennis after a 6-2 7-5 quarter-final defeat to Chile's Nicolas Massu.
Massu will now face Taylor Dent in the semi-finals after the American defeated Tomas Berdych of the Czech Republic.
Fellow Chilean Fernando Gonzalez beat France's eighth seed Sebastien Grosjean to book a semi-final with Mardy Fish.
The results mean Chile will win their first tennis medal since the sport became part of the Games.
Dent saw off the Berdych, who defeated world number one Roger Federer on Tuesday, 6-4 6-1 while Fish defeated Russia's Mikhail Youzhny 6-3 6-4.
In the women's singles, Russia's Anastasia Myskina booked her place in the semi-finals with a comfortable straight sets win over Francesca Schiavone.
The French Open champion lost just three games on her way to a 6-1 6-2 victory over her Italian opponent.
She will meet Belgian Justine Henin-Hardenne after the gold-medal favourite defeated France's Mary Pierce 6-4 6-4.
There was another upset when Japan's eighth seed Ai Sugiyama was beaten 6-3 6-4 by Australia's Alicia Molik.
France's second seed Amelie Mauresmo maintained her quest for a medal with a 7-6 4-6 6-2 win over Russian fifth seed Svetlana Kuznetsova and will now play Molik for a place in the final.
In the women's doubles, fifth-seeded Shinobu Asagoe and Ai Sugiyama of Japan eliminated third-seeded Martina Navratilova and Lisa Raymond of the United States 6-4 4-6 6-4 in the quarter-finals.
The defeat could mark the end of Navratilova's long and illustrious career.