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 "Whooo!"
A schedule backlog transformed the Olympics at Wimbledon into a parade of Grand Slam champions Monday, with the Williams sisters and Roger Federer all playing at the same time.
And all won.
"I just wanted to play well for my country," Venus Williams said. "It was just great to be out there."
She 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-Mihaela 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."
The U.S. team went 5-0, with John Isner and Varvara Lepchenko also advancing. Lepchenko completed a rain-interrupted, two-day, first-round win over Veronica Cepede Royg of Paraguay, 7-5, 6-7 (6), 6-2.
Venus Williams, who is 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.
"I've been working really hard on my serve," she said. "I really haven't had my serve where I wanted it this year. But I definitely worked a lot on it, so that way it would be a real weapon for me, which is what I'm used to."
Despite being diagnosed last year with an autoimmune disease that can cause fatigue, she 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, Williams will have to play six consecutive days if she reaches Saturday's final.
"I definitely expect everything to be tough on me almost nowadays," Williams 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.
Serena will next play Vera Zvonareva of Russia, the Wimbledon runner-up in 2010.
Information from The Associated Press was used in this report.