Six-time champion Federer beat David Nalbandian 6-4, 6-2, 6-4 to move closer to equaling the record of seven Wimbledon singles titles held by Pete Sampras and 1880s player Willie Renshaw.

Two-time winner and defending champion Rafael Nadal committed only three unforced errors in a 7-6 (6), 7-6 (5), 6-0 victory over Gilles Muller, a 92nd-ranked wild card from Luxembourg.

Second-seeded Novak Djokovic also advanced to the fourth round with a 6-4, 4-6, 6-3, 6-4 win over Marcos Baghdatis of Cyprus.

The two-time semifinalist from Serbia won 43 straight matches heading into the French Open but lost to Roger Federer in the semifinals. Since that loss, Djokovic has won three straight at the All England Club. Djokovic, a two-time Australian Open champion, will face Michael Llodra of France on Monday.

Fifth seed Robin Soderling lost 6-1 6-4 7-5 to Australian qualifier Bernard Tomic in the biggest upset so far in this year's men's singles at Wimbledon.

The 18-year-old Tomic, poised to end Lleyton Hewitt's 11-year reign as Australian No.1, stunned Soderling who fought back from two sets down to beat Hewitt in the last round.

Tomic will play Jurgen Melzer or Xavier Malisse in the last 16.

Williams, chasing a third straight title and fifth overall in her comeback from nearly a year out with serious health problems, served 10 aces in beating 26th-seeded Maria Kirilenko 6-3, 6-2.

Another former champion, 2004 winner Maria Sharapova, also reached the round of 16, downing Klara Zakopalova of the Czech Republic 6-2, 6-3.

Other winners included top-ranked woman Caroline Wozniacki, former US Open champion Juthen won six straight games, finishing with an ace.

It's the first time Nadal has advanced to the round of 16 here without losing a set.

Nadal said he felt discomfort in his right leg, but that it was not related to the two heavy falls he took at the baseline during the match.

"I started to feel the leg a little bit more tired than usual," he said. "But I played today without problems, and now I (have) one day and a half to rest and recover. I hope it will be perfect for Monday." That's when Nadal will face Del Potro, who beat Gilles Simon 7-6 (8), 7-6 (5), 7-5 and showed he is nearing top form after missing most of 2010 after surgery on his right wrist.

"He's a fantastic player. He's one of the best players of the world," Nadal said. "It will be a fantastic test and I have to be playing my best if I want to have chances." Williams picked up her first straight-set win in five matches since she returned this month after being away from the tour for nearly a year because of a series of health scares, including blood clots in her lungs.

The seventh-seeded American is trying to become the first woman since Steffi Graf in 1991-93 to win three consecutive titles at the All England Club.

Against Kirilenko, Williams saved the only break point she faced and put together a 32-9 edge in winners.

"The matches are getting better, my serve is getting better, so it's just getting the rhythm that I've been missing a little bit, and it's good," Williams said. "I just want to continue to serve better like I did today, and just hold on out there and just move, and just really more than anything enjoy myself and stay focused." Williams next faces 2007 Wimbledon runner-up Marion Bartoli, the ninth-seeded Frenchwoman who beat Flavia Pennetta 5-7, 6-4, 9-7.

Sharapova, the only champion in the women's draw other than the Williams sisters, struggled with her game but still progressed relatively easily against Zakopalova. The fifth-seeded Russian - watched by her fiance, New Jersey Nets guard Sasha Vujacic - had 21 unforced errors and four double-faults in an inconsistent baseline performance in the wind on Court 2.

But, after falling behind 3-1 in the second set, Sharapova lifted her game to win five games in a row to finish off the 35th-ranked Czech player.

Sharapova hasn't reached the semifinals since 2006. She will next face 20th-seeded Peng Shuai of China, who beat Melinda Czink of Hungary 6-2, 7-6 (5).

Wozniacki, still looking for her first Grand Slam title, swept Jarmila Gajdosova 6-3, 6-2 to make the fourth round for the third straight year. Wimbledon is the only major championship in which the Dane has not reached at least the quarterfinals.

Sixth-seeded Francesca Schiavone, the 2010 French Open champion, lost to Tamira Paszek of Austria in a three-set marathon 3-6, 6-4, 11-9.

Berdych, the sixth-seeded Czech, needed only seven points to complete a 6-2, 6-4, 6-3 win over Alex Bogomolov Jr. of the United States. The match had been suspended because of rain with Berdych leading 4-3, 15-0 in the third set Friday.

Berdych will next play 10th-seeded Mardy Fish, the last American man left in the tournament. He advanced when Robin Haase retired at 1-1 in the fourth set because of injuries.

Fish was up two sets to one, 6-3, 6-7 (5), 6-2.

Ninth-seeded Gael Monfils lost to 93rd-ranked Polish qualifier Lukasz Kubot 6-3, 3-6, 6-3, 6-3. Kubot, who won three qualifying matches to get into the main draw, is the first Pole to reach the fourth round here since Wojtek Fibak in 1981.

No. 18 Ana Ivanovic, a former top-ranked player and 2008 French Open champion, was knocked out by Petra Cetkovska, 6-2, 7-6 (0).