London :Venus Williams battled her way into the Wimbledon quarter-finals on Monday as her younger sister Serena squared up against Maria Sharapova and fourth seed Jelena Jankovic crashed out.
Venus Williams, a five-time Wimbledon champion, saw off a gritty fightback from Australia's Jarmila Groth to go through to the last eight.
But while the world number two progressed, former world number one Jankovic was the first big name to tumble out of the championships as she pulled out of her clash with Russian 21st seed Vera Zvonareva.
Jankovic, who has now fallen at the fourth round here four times in five years, was 6-1, 3-0 down when she withdrew.
The Williams sisters had had a fairly easy ride to the round of 16, dropping no sets and few games.
But Venus was given a rough ride by the determined, unseeded Australian number three in a 6-4, 7-6 (7/5) win on Court Two.
Slovak-born Groth entered the match in good form, having reached a Grand Slam fourth round for the first time at the French Open and followed up her exploits on clay by doing the same here on grass.
Williams was twice broken in the second set and had to dig deep to take it to a tie break and then win it.
Meanwhile China's Li Na reached the last eight for the second time as she beat skilful Polish seventh seed Agnieszka Radwanska.
Li, the ninth seed, won 6-3, 6-2 and has yet to drop a set in her campaign so far.
The Chinese number one is aiming to replicate her best-ever Grand Slam run, which took her to the Australian Open semi-finals earlier this year.
Li faces the winner of the clash between defending champion Serena Williams and Maria Sharapova, who made her name when she won the 2004 title here.
The Russian 16th seed has spent a long time struggling with a shoulder injury but is finally feeling back in the groove and could give the American world number one plenty to think about.
Meanwhile many will be watching the clash of the Belgian comeback queens, Kim Clijsters and Justine Henin, who are both looking to add the Wimbledon crown to their slew of Grand Slam titles.
Both former world number ones have returned from retirement and will have to put their friendship on hold during the Court One clash.
The pair have 12 wins each from their 24 meetings, but Clijsters should be confident of progressing.
She has beaten Henin twice already this year and is yet to drop a set in her first three matches back at the All England Club after a four-year absence following a premature decision, as it turned out, to retire.
Danish third seed Caroline Wozniacki takes on the Czech Republic's Petra Kvitova.
French 11th seed Marion Bartoli, who reached the 2007 final here, is up against Bulgarian Tsvetana Pironkova.
Meanwhile Klara Zakopalova faces Estonian qualifier Kaia Kanepi.