Roger Federer has failed in his third attempt to win an Olympic medal, suffering a shock straight-sets defeat by US player James Blake on Thursday.
The eighth-seeded Blake knocked Federer out in the quarterfinals, winning 6-4, 7-6.
It was the first time Blake had ever beaten the Swiss champion. In their previous eight matches he had only taken one set off Federer.
The game was delayed by rain for over three hours, and commentators say Federer seemed off form from the beginning. His forehand was unreliable, he struggled to hold serve and made unforced errors in the tie break which ended the match.
Federer's defeat was the first upset in the men's singles in the Beijing Olympics.
Blake, playing in his first Olympics, is the only US player left in contention.
Ahead of the match, Federer described Blake as "always extremely dangerous to play against".
"It's a big disappointment, obviously," he told journalists after the match. "The Olympics was one of the goals of the season for me."
"I think James played well... I've played him on many occasions, but I think this was the best I've seen him. I'm happy for him. I hope he can go all the way now."
Blake said afterwards that Federer was under tremendous pressure as he had history to contend with as well as the game in hand. He paid warm tribute to the Swiss champion.
"You never see him lose his cool. I still have a ton of praise for him. I still have a ton of respect for him as a man," he said.
Federer, who loses his world number one ranking to his great Spanish rival Rafael Nadal on Monday, has failed to win any major championships this year.
In the 2004 Olympics in Athens he was eliminated in the second round, and in the 2000 Sydney games he failed to get beyond the semifinals.
Before coming to Beijing he said that an Olympic victory, or success at the US Open, would "save" his season.
He still has a chance of an Olympic medal, however: he has reached the doubles quarterfinal with his partner Stanislas Wawrinka.
The match, opposing them to the Indian pair Mahesh Bhupathi and Leander Paes, was supposed to follow shortly after the singles match, but had to be rescheduled to Friday because of rain.
swissinfo with agencies
Roger Federer was born on August 8, 1981 in Binningen, canton Basel Country.
His father is Swiss German, and his mother South African.
He speaks three languages fluently: German, French and English. At home he uses Swiss German.
Federer's partner since 2000 is former tennis professional Miroslava "Mirka" Vavrinec, who retired in 2002 and is now his manager.
He holds numerous tennis records, including as the man to have stayed at the number one ranking for the longest unbroken period.
He shares with Bjorn Borg the distinction of being the only man to have won five consecutive Wimbledon titles.
Two major feats have eluded him: a French Open title and an Olympic singles medal.
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