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!"

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.

"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.

Other major champions to advance on a cool, sunny day included three-time Olympian Lleyton Hewitt, top-seeded Victoria Azarenka and three-time Wimbledon runner-up Andy Roddick.

The U.S. team went 5-0, 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.

"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.

Roddick converted only two of 13 break-point chances against Klizan but dominated with his serve, as often happens at Wimbledon, where he's a three-time runner-up.

"I served really well," he said. "I would have liked to have converted more break points. But I got a couple and, thankfully, that's all I needed."

The Olympic match, delayed a day by rain, was Roddick's first in eight years. He lost in the third round at the 2004 Games and skipped Beijing in 2008.

Roddick, a dedicated Davis Cup player for the United States, took Court 2 on a sunny morning looking particularly patriotic. He wore a blue shirt, white shorts and stars-and-stripes shoes.

"Posh sneakers, Andy," shouted a spectator with a British accent.

He lost only nine points in 11 service games, and the first break point came on the final shot of the opening set, which put him ahead to stay.

Roddick won with more than just his serve, hitting several improbable shots, including a back-to-the-net lob to help win one point, and a backhand as he did a belly flop behind the baseline.

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