Returning to grand slam tennis after a year out with health problems, Serena Williams opened the defense of her Wimbledon title by beating Aravane Rezai in three sets - then burst into tears on Centre Court in London.

After serving her 13th ace to close out a 6-3, 3-6, 6-1 win, Williams buried her face in her towel and sobbed as she sat on 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 on 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."

Williams fought through a mid-match slump, re-establishing her authority in the third set with her big serve and powerful groundstrokes. She showed why she is still considered a title favorite despite her long absence.

"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.

Williams finished with 24 winners and 18 unforced errors, compared to 22 each for the Frenchwoman.

Classic dress

In keeping with Wimbledon tradition, Williams opened play on Day 2 on Centre Court at the All England Club 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 as hard as she could, 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. She lost the momentum in the second set, and Rezai broke in the sixth game to force a third set.

In other matches, three-time Wimbledon runner-up Andy 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 advance.

Juan Martin del Potro, the 2009 US 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 on Monday, then won 11 of the 15 games yesterday.

Former top-ranked Jelena Jankovic was eliminated in the first round, losing to 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.

Among the women's players advancing were No. 8 Petra Kvitova, No. 11 Andrea Petkovic and No. 14 Anastasia Pavlyuchenkova.

Men's winners included No. 15 Gilles Simon.

Serena and her older sister Venus, a five-time champion, have won nine of the last 11 Wimbledon titles. Venus, who was off for nearly five months with a hip injury, is in the opposite half of the draw and could face her sister in the final.

Venus next faces 40-year-old Kimiko Date-Krumm, who is back in the second round at Wimbledon 15 years after she reached the semifinals and three years after coming out of a long retirement.

"It was amazing when she came back," Williams said of Date-Krumm. "I watched her results. She's been playing so well."