Mark Humphrey, Associated Press
WIMBLEDON, England — Four-time Olympian Venus Williams walked off Wimbledon's cozy Court 2 gleefully waving her fist as fans chanted, "U-S-A! U-S-A!"
Twenty minutes later, at the other end of the All England Club, Serena Williams departed Court 1 with a triumphant grin and a shout of "Wooo!"
Ten minutes after that, Roger Federer closed out his latest Centre Court victory in pursuit of his first career singles gold medal.
A schedule backlog transformed the Olympics at Wimbledon into a parade of Grand Slam champions Monday, with the Williams sisters and Federer all playing at the same time.
And all won.
"What a good day for fans between me, Venus, Roger and all the other players," Serena Williams said. "It's really such a great experience."
Venus Williams waited an extra day because of rain to begin her bid for a record fourth gold medal in Olympic tennis, then defeated recent French Open runner-up Sara Errani of Italy 6-3, 6-1.
Serena completed a July sweep of Poland's Radwanska sisters by beating Urszula in the second round, 6-2, 6-3. Federer also reached the third round, beating Julien Benneteau of France 6-2, 6-2.
After winning in singles, the Williams sisters began a bid for their third Olympic doubles gold medal by eliminating Sorana Cirstea and Simona Halep of Romania 6-3, 6-2. They won in 2000 and 2008.
"Another gold medal would be amazing," Venus said. "I can't even imagine the feeling. I think my head would be too big, and no one would even like me anymore."
Other major champions to advance in singles on a cool, sunny day included three-time Olympian Lleyton Hewitt, top-seeded Victoria Azarenka, Kim Clijsters, Petra Kvitova, Ana Ivanovic and three-time Wimbledon runner-up Andy Roddick.
The U.S. team went 6-0, with John Isner and Varvara Lepchenko also advancing. Isner, seeded 10th, hit 15 aces and reached the third round by beating Malek Jaziri of Tunisia 7-6 (1), 6-2. Lepchenko completed a rain-interrupted, two-day, first-round win over Veronica Cepede Royg of Paraguay 7-5, 6-7 (6), 6-2.
Roddick's victory set up the first showdown of the tournament. As a price for being unseeded, he'll face 2011 Wimbledon champion Novak Djokovic on Tuesday.
"That's my own fault," Roddick said. "It's tough. That's obviously not an ideal situation, but I'm sure he's not thrilled about it either."
Venus Williams, also unseeded, drew a tough first-round foe in Errani, who has won four titles this year and is ranked a career-high No. 9. Williams served well, charged the net aggressively and appeared at ease on the Wimbledon grass, where she has won five of her seven Grand Slam titles.
Afterward, Williams challenged the Olympic record for references to herself in the third person.
"Today definitely seemed a lot more like classic Venus," she said. "I know she's in here, but she has a couple of things she's dealing with, so she does the best she can."
Despite being diagnosed last year with an autoimmune disease that can cause fatigue, Williams began 2012 determined to make the Olympic team. She won the gold in singles at the 2000 Games and teamed with Serena to take the gold in doubles in 2000 and 2008.
Because her opening match was delayed a day by rain, Venus will have to play six consecutive days if she reaches Saturday's final.
"I definitely expect everything to be tough on me almost nowadays," she said.
Over on Court 1, Serena's serve lacked its usual sizzle, and she was even broken once, but she still eliminated Radwanska with little drama. She defeated Radwanska's sister, Agnieszka, in the Wimbledon final this month.
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