WIMBLEDON, England -- Playing Olympic tennis twice a day proved too much for Venus Williams, and her workload at Wimbledon now will be a lot lighter.
Williams squandered a lead in each set Wednesday and lost her third-round match to No. 7-seeded Angelique Kerber of Germany, 7-6 (5), 7-6 (5).
Seeking a record fourth gold medal in Olympic tennis, Williams still has a shot with sister Serena in doubles. They play in the quarterfinals Thursday.
Venus looked sharp in the first two rounds of singles this week, as if rejuvenated by the Wimbledon setting, where she has won five of her seven Grand Slam titles. But she was diagnosed last year with an autoimmune disease that causes fatigue, and she looked weary against Kerber.
In the first set Williams failed to convert three set points, then blew a 5-1 lead in the tiebreaker. She was up 3-1 in the second set, but Kerber again charged back.
"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 U.S. Open last year, is ranked a career-high No. 7. She advanced to the quarterfinals against top-seeded 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."
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."
Kerber played boldly at key moments, and the left-hander saved three set points serving at 4-5 in the first set. Williams again seemed on the verge of winning the set at 5-1 in the tiebreaker, but she then lost six consecutive points, the last when she sailed an easy forehand long.
Williams looked to the sky in disbelief as she walked to her chair. Once she sat down, she hung her head and squeezed her forehead as if trying to erase the memory of what had just happened.
She let another lead slip away in the second set, and her potent serve let her down. She double-faulted twice in the last tiebreaker, the second time to give a match point to Kerber, who coolly finished off Williams with a service winner.
Williams, a four-time Olympian at 32, won her only singles medal -- a gold -- in 2000.
"Hopefully, there's 2016," she said.
Serena Williams worked under Wimbledon's roof during a brief midday shower, and the conditions clearly suited her. She whacked winners even from behind the baseline, and more than once spun on one foot after smacking a shot, mixing a little body English with plenty of brute force.
Williams hit a Wimbledon record 102 aces en route to her fifth title at the All England Club last month, and the shot remains a dominant force, especially on grass. She hit three consecutive aces against Zvonareva and lost only seven points in six service games.
In the second set, the crowd tried to coax a comeback from the Russian, who won the bronze in 2008. But when she began tossing her racket in frustration, cheers for her turned to jeers.
And fans applauded Williams' domination.
"We love you, Serena!" a spectator near the top of the stadium shouted during the final changeover. Williams continued to stare sternly, but she wore a grin moments later as she walked off the court in triumph, waving to the stands dotted with U.S. flags.
Information from The Associated Press was used in this report.