WIMBLEDON, England -- Wimbledon already has lost its top-four seeded women's players, while the Williams sisters keep rolling toward another sibling final. Roger Federer and Rafael Nadal also are closing in on another title matchup.

Yesterday's fourth-round play at the All England Club produced more upsets at the top of the women's seedings but also offered more convincing wins from the champions and title contenders.

Second-seeded Jelena Jankovic, hobbled by a knee injury, fell 6-3, 6-2 to Tamarine Tanasugarn. No. 4 Svetlana Kuznetsova, the 2004 U.S. Open champion, lost 6-4, 1-6, 7-5 to 19-year-old Agnieszka Radwanska.

With top-seeded Ana Ivanovic and No. 3 Maria Sharapova eliminated last week, none of the top four seeded women reached the quarterfinals -- the first time that's happened at Wimbledon and also the first time at any Grand Slam tournament in the 40-year history of the Open era.

The highest women's seeded player left is No. 5 Elena Dementieva, who cruised to a 6-2, 6-1 win over Shahar Peer. Only three of the top 14 seeded women are left.

The other two are the Williams sisters, and they posted back-to-back victories on Court 2 -- nicknamed the "Graveyard of Champions" for its history of upsets. They questioned why they weren't put on Centre Court or Court 1.

Defending champion and seventh-seeded Venus Williams beat teenager Alisa Kleybanova 6-3, 6-4, and two-time winner and No. 6 Serena downed Bethanie Mattek -- the only other American left in the men's or women's draw -- 6-3, 6-3.

"It wasn't what I would have liked to see," Serena Williams said of the Court 2 scheduling. "Initially, I thought, 'Is this the right schedule?' I thought maybe there was a mistake. But I can't dwell on that. I just have to focus on doing the best that I can whether I'm on Court 2 or Court 20."

Between them, four-time champion Venus and two-time winner Serena have won six of the past eight women's singles titles at Wimbledon. They're in opposite halves of the draw and could meet in the final Saturday. The Williams sisters faced each other in the 2002 and'03 finals, with Serena winning both.

In men's play, Federer swept Lleyton Hewitt -- the last man to win the title before Federer's run of five straight titles -- 7-6 (9-7), 6-2, 6-4 to extend his winning streak on grass to 63 matches and 38 in a row at the All England Club.

Federer next will face the last player to beat him on grass and at Wimbledon -- Mario Ancic, who won in the first round in 2002. Ancic came from two sets down yesterday to beat Fernando Verdasco 3-6, 4-6, 6-3, 6-4, 13-11. The final set lasted 95 minutes.

No. 2-ranked Nadal, runner-up to Federer the past two years, overcame an injury scare in the second game to defeat Mikhail Youzhny 6-3, 6-3, 6-1.

Nadal slipped on the worn turf behind the baseline on Court 1 while stretching to hit a forehand, with his right leg bending awkwardly. After losing the point, he took a medical timeout, and a trainer wrapped his leg below the knee. Nadal lost the next point and the game, but he showed no sign of trouble and dominated the rest of the way.

Nadal's quarterfinal opponent will be Britain's Andy Murray, who came from two sets down to beat No. 8 Richard Gasquet 5-7, 3-6, 7-6 (7-3), 6-2, 6-4 in a Centre Court match that ended in near-darkness at 9:30 p.m.

No. 10-seeded Marcos Baghdatis, a semifinalist in 2006 and quarterfinalist last year, squandered three match points in the fifth set. He lost 5-7, 6-2, 3-6, 7-6 (7-4), 8-6 to Feliciano Lopez, who, down 0-40 at 4-5, came up with big serves on all three points to avoid defeat.

Also advancing among the men were former No. 1 Marat Safin, who beat No. 13 Stanislas Wawrinka in four sets; Rainer Schuettler, the oldest remaining player in the draw at age 32, who downed Janko Tipsarevic in four sets; and 145th-ranked Arnaud Clement, who beat Marin Cilic, 19, in straight sets to become the lowest-ranked player to reach the men's quarters here since No. 198 Alexander Popp in 2003.

On the women's side, wild card Zheng Jie followed her upset of Ivanovic last week by beating 19-year-old Agnes Szavay 6-3, 6-4. Other women's winners were Nicole Vaidisova, who downed No. 8 Anna Chakvetadze 4-6, 7-6 (7-0), 6-3, and Nadia Petrova, a 6-1, 6-4 victor over Alla Kudryavtseva, who had beaten Sharapova in the second round.