Venus Williams is out of the women's draw at the London Olympics after crashing in straight sets to Angelique Kerber.
Williams squandered a lead in each set on Wednesday and lost her third-round match to No.7-seeded German 7-6 (5) and 7-6 (5).
Seeking a record fourth gold medal in Olympic tennis, Williams still has a shot with sister Serena in the doubles. They play in the quarterfinals on Thursday.
"I made a few errors and she hit a few winners, and things can go quickly in tennis," Williams said.
Kerber, a semifinalist at Wimbledon last month and at the US Open last year, is ranked a career-high No. 7. She advances to the quarter-finals where she will meet top-seed Victoria Azarenka of Belarus.
"She had a lot of answers," Williams said. "She's having a great year, and I have to give her credit for playing well."
Like Williams, Roger Federer is also down to one shot at a medal. He advanced to the quarter-finals in singles but lost with Swiss teammate Stanislas Wawrinka in doubles.
Earlier Wednesday, Serena Williams hit 12 aces and repeatedly rocketed her groundstrokes past No. 13-seeded Vera Zvonareva to win 6-1, 6-0. Swinging lustily with almost every shot, No. 4-seeded Serena hit 32 winners to three for the Russian, who also lost when they met in the 2010 Wimbledon final.
The younger Williams swept the final 10 games and was done in only 51 minutes.
"I was just playing unbelievable," Williams said. "I was nervous going into the match and I didn't speak to anyone and I had a bad practice. I had no idea I would play like this."
Men's No. 3 Andy Murray of Britain rallied past Marcos Baghdatis of Cyprus 4-6, 6-1 and 6-4. American John Isner, seeded No. 10, beat No. 7 Janko Tipsarevic of Serbia 7-5 and 7-6 (14) and will face Federer on Thursday.
Four-time Grand Slam champion Kim Clijsters, playing in her first Olympics weeks before she retires, beat former No. 1 Ana Ivanovic of Serbia. Her opponent Thursday will be first-time Olympian Maria Sharapova, who rallied past No. 15-seeded Sabine Lisicki of Germany, 6-7 (8), 6-4 and 6-3.
Azarenka eliminated No. 16 Nadia Petrova of Russia.
Federer, seeded No. 1, endured two rain delays and a shaky moment late in the first set to beat Denis Istomin of Uzbekistan 7-5, 6-3. The four-time Olympian has yet to win a singles medal.
Serving at 5-all in the first set, Federer faced three break points and erased them all. He then broke and was in control from there.
Federer and Wawrinka later lost to unseeded Jonathan Erlich and Andy Ram of Israel, 1-6, 7-6 (5) and 6-3. Federer and Wawrinka won the gold in doubles in 2008.