WIMBLEDON, England -- Returning to Grand Slam tennis after a year away with health problems, Serena Williams opened her Wimbledon title defense Tuesday by beating Aravane Rezai in three sets -- then burst into tears on Centre Court.

After serving her 13th ace to close a 6-3, 3-6, 6-1 victory, Williams buried her face in her towel and sobbed from her courtside chair. She was still crying as she left the court, overcome with emotion after enduring a long layoff that included two foot operations and treatment for blood clots in her lungs.

"I usually don't cry ... but it's just been so hard," the four-time Wimbledon champion said. "I never dreamt I would be here right now. And then to win. I just wanted to win at least one match here."

Following Williams on Centre Court was Roger Federer, who began his chase for a record-equaling seventh Wimbledon championship by beating Mikhail Kukushkin of Kazakhstan 7-6 (2), 6-4, 6-2 in the wind.

Second-seeded Novak Djokovic, playing for the first time since his 43-match winning streak was stopped by Federer at the French Open, sailed into the second round with a 6-4, 6-1, 6-1 victory over Jeremy Chardy of France. Djokovic dropped only 11 points on serve.

Other winners included three-time Wimbledon runner-up Andy Roddick and Juan Martin del Potro. Among the women, top-seeded Caroline Wozniacki made a strong start in her latest bid for her Grand Slam title, while former No. 1 Jelena Jankovic lost in the first round.

No. 10 Samantha Stosur became the highest seeded player eliminated, falling 6-3, 6-4 to Hungary's Melinda Czink -- the lowest-ranked woman in the draw at No. 262.

Williams fought through a midmatch slump, then reasserted command over her French opponent in the third set with a big serve and powerful groundstrokes. She showed why she is still considered a title favorite despite her long absence and her No. 7 seeding.

"It's been a disaster year, but I've been praying," Williams said. "To be able to come back at Wimbledon is pretty awesome. I didn't expect to play. And I didn't expect to even do anything. So I'm just excited. I've never cried with joy for anything."

After losing the second set, Williams took charge in the final set, winning the last five games.

"I kept thinking, 'This is Wimbledon,"' she said.

The point of the match came at 3-1, when Williams stretched for a backhand at the baseline and fell over as she hit a winning lob over Rezai at the net. Rezai said she saw the tears in Williams' eyes when they shook hands after the match.

"It definitely was so emotional for me because throughout the last 12 months, I've been through a lot of things that's not normal, things you guys don't even know about," Williams said. "It's just been a long, arduous road. To stand up still is pretty awesome."

Rezai was impressed by Williams' play and touched by her outpouring.

"It shows she's not a machine, she's a human being," Rezai said. "We all have a heart, we all have emotions. ... If she wins the next two or three matches, I think she can win the tournament."

In keeping with Wimbledon tradition, Williams opened play on Day 2 on Centre Court as the women's defending champion. She strode onto court wearing a cardigan, and played in a classic dress with blue trim. Her fingernails were painted in the Wimbledon colors of purple and green.

The 61st-ranked Rezai came out hitting hard, breaking Williams in the first game that lasted nine minutes and going up 2-0. But Williams then won five games in a row and took the set with only four unforced errors. Williams lost the momentum in the second set, and Rezai broke in the sixth game to force a third set.

Williams said it was the most emotional she's ever felt after a victory -- and this was only a first-round match.

"For me it wasn't about winning the match," she said. "It was about being out there. ... It just really goes to show if you don't give up, you still have a chance. I guess I proved that I could, that I could. I think that sums it up: I could."

Federer never lost serve, saving all three break points, and won 29 of 31 of his points on serve in the first set. The third-seeded Swiss piled up 53 winners -- 37 more than Kukushkin, who was making his Wimbledon debut.

Federer, a 16-time Grand Slam winner who lost in the Wimbledon quarterfinals last year, is looking to equal Pete Sampras' seven titles at the All England Club.

"The first match at Wimbledon is never easy really because we don't get any practice time on Centre Court," Federer said. "I thought I struggled putting enough returns into play in the first set but I thought he played well. For a set and a half he made it hard for me. I also served really well so I was very pleased with the match."

Roddick served 30 aces -- including four in a row in one game -- and beat German qualifier Andreas Beck 6-4, 7-6 (6), 6-3 to reach the second round.

"I feel healthy," Roddick said. "I know what it takes to go deep at this tennis tournament."

Del Potro, the 2009 U.S. Open champion, downed Flavio Cipolla of Italy 6-1, 6-4, 6-3. The 24th-seeded Argentine led Cipolla 6-1, 1-3 when rain suspended play Monday, then won 11 of the 15 games played Tuesday.

On Court 1, Wozniacki defeated Arantxa Parra Santonja of Spain 6-2, 6-1. The 20-year-old Dane had fewer winners than her opponent, but made only five unforced errors.

Jankovic was beaten by Maria Jose Martinez Sanchez of Spain 5-7, 6-4, 6-3. The 15th-seeded Serb reached the fourth round at the All England Club last year.

Also advancing among the women were No. 4 Victoria Azarenka, No. 8 Petra Kvitova, No. 11 Andrea Petkovic and No. 14 Anastasia Pavlyuchenkova. Men's winners included No. 7 David Ferrer, No. 13 Viktor Troicki, No. 15 Gilles Simon and No. 21 Fernando Verdasco.