Serena Williams breaks out in win at Wimbledon; Roger Federer, Rafael Nadal advance

It’s as if Serena Williams is unpacking her tennis game bit by bit, taking it out of the luggage slowly.

Remove the forehand; shake out the wrinkles. Unfold the backhand; make sure there are no unexpected holes. Dig around and find the serve — the one that sends chalk dust into the air, the one that can make an opponent cringe even before the ball hits the ground.

Williams, the defending Wimbledon champion but only the No. 7-seeded player in the women’s draw because she sat out most of the last year with injuries and illness, moved briskly into the fourth round Saturday.

The 29-year-old pounded 10 aces, faced only one break point and beat 26th-seeded Russian Maria Kirilenko, 6-3, 6-2, in 1 hour 30 minutes.

With the win, Serena Williams joined her 31-year-old sister, Venus Williams, in the fourth round and kept alive the possibility that the sisters, who have combined to win nine of the last 11 Wimbledon titles, might meet in the women’s final.

Serena Williams will play ninth-seeded Marion Bartoli of France in Monday’s fourth round. Bartoli should be thankful that there is no play Sunday because she needed 3 hours 9 minutes to beat Italy’s Flavia Pennetta, 5-7, 6-4, 9-7.

The biggest upset of the tournament so far on the men’s side happened Saturday, when 18-year-old Bernard Tomic of Australia wore out fifth-seeded Robin Soderling of Sweden. Soderling complained of an upset stomach and needed a trainer during his 6-1, 6-4, 7-5 loss.

Mardy Fish, 31 years old and seeded 10th, is the only American man to make it into the fourth round, outlasting Robin Haase of the Netherlands, 6-3, 6-7 (5), 6-1, 1-1, retired.

Six-time Wimbledon champion Roger Federer, seeded No. 3, had no trouble beating 2002 Wimbledon finalist David Nalbandian, 6-4, 6-2, 6-4, but second-seeded Novak Djokovic needed to smash a racket to smithereens and took four sets to defeat flashy shot maker Marcos Baghdatis, 6-4, 4-6, 6-3, 6-4.

Also moving mostly unchallenged into the fourth round Saturday were top-seeded Caroline Wozniacki and fifth-seeded Maria Sharapova, the 2005 champion.

Perhaps the most attractive fourth-round match of the tournament will be top-seeded Rafael Nadal, the defending champion, against 24th-seeded Juan Martin del Potro.

After Nadal completed a 7-6 (6), 7-6 (5), 6-0 win over Gilles Muller, he lamented his bad fortune in drawing 2009 U.S. Open finalist del Potro so early in the tournament.

“His ranking for sure is much better than what the rankings say,” Nadal said of the Argentine who sat out much of last season recovering from wrist surgery. “I’m not lucky to play against del Potro in the round of 16. But that’s what it is, and I have to be playing my best tennis to try to win.”

Williams is coming closer to playing her best tennis. She really seized Saturday’s match in the third game of the second set, one that lasted 14 points and one in which Williams gained a service break by hitting harder and harder and harder.

“It’s the best I’ve played since I came back,” the four-time Wimbledon champion said. She compared her ongoing comeback to falling off a bicycle and getting back on, which, she said, she did last fall.

“I fell — I literally fell — off the bicycle, actually, and I have a horrible scar on my shoulder from it,” Williams said. “It was painful, but I was able to recover. I got back on that bike, and I rode home. So I’m back here playing again.”

Williams said the bike in question was a pink beach cruiser with fat tires and big handlebars.

If her injuries and accidents made 2010 a mostly forgettable year, Williams said there’s one good thing that’s happened since.

“I’m here, and I’m alive,” she said. “And I don’t take any moment for granted.”

diane.pucin@latimes.com

twitter.com/mepucin