WIMBLEDON, England — While Roger Federer glided to another victory on Center Court, and Rafael Nadal won despite a scary stumble on Court 1, the Williams sisters found themselves playing back to back Monday on cozy, clattery Court 2, known as the "Graveyard of Champions."

"It wasn't what I would have liked to see," Serena Williams said. "Initially I thought, 'OK, is this the right schedule?' I thought maybe there was a mistake."

The sisters' mother and coach, Oracene Price, suspected more than a mere mistake by organizers.

"I guess they wanted to put them on the jinx court so they could lose," Price said.

Even after Venus and Serena spent the day at the Graveyard, their title hopes remained very much alive. Four-time champion Venus played first, beating Alisa Kleybanova 6-3, 6-4. Ninety minutes later, two-time champion Serena joined her older sister in the quarterfinals by beating fellow American Bethanie Mattek 6-3, 6-3.

The fourth round Monday claimed No. 2 Jelena Jankovic and No. 4 Svetlana Kuznetsova, leaving No. 5 Elena Dementieva as the highest-seeded survivor. Jankovic, slowed by a knee injury she suffered in the previous round, lost to Tamarine Tanasugarn 6-3, 6-2. Kuznetsova was beaten by Agnieszka Radwanska 6-4, 1-6, 7-5.

"Every player is ready to play, especially at these Slams," Venus Williams said.

Almost as unpredictable is the men's draw, with eight of the top 10

While five-time defending champion Federer beat Lleyton Hewitt 7-6 (7), 6-2, 6-4, Nadal hurt his right leg during the second game against Mikhail Youzhny. He slipped on worn turf behind the baseline.

"I felt a little bit pain," he said. "I was a little bit scared."

After the trainer wrapped his leg below the knee, Nadal showed no sign the injury bothered him the rest of the way, winning 6-3, 6-3, 6-1.

"I am fine," Nadal said.