Both sisters, who have met in four of the last five Grand Slam finals with Serena victorious each time, were forced to three sets in tough quarterfinals.

World number one Serena in particular found herself in trouble against Jennifer Capriati. But despite 36 unforced errors she managed to recover from a set down to win 2-6, 6-2, 6-3 in 1hr 40min.

Venus was a 6-2, 2-6, 6-1 over 1999 champion Lindsay Davenport, who revealed she may have played her last game at the All England Club.

Serena's reward for battling through was a semifinal with third seed Justine Henin-Hardenne that has all the makings of a grudge match.

Henin-Hardenne knocked the younger of the Williams sisters out of the French Open at the same stage last month, taking full advantage of the support of a wildly partisan crowd which booed Serena off court.

Henin-Hardenne had the easiest ride of the four semifinalists, swatting 33rd seed Svetlana Kuznetsova of Russia 6-2, 6-2.

Her compatriot Kim Clijsters, the second seed, had her concentration stung by a sting from a bee and dropped the first set to Italy's Silvia Farina Elia.

But she managed to recover to win 5-7, 6-0, 6-1 and set up her clash with Venus Williams.

Serena admitted Capriati had given her a serious fright. "It was definitely tough," she said. "I knew I was in for a match. I just had to come back. I at least wanted to go three sets if I could."

Capriati drew some comfort from pushing her opponent to the limit.

"She had to elevate her game. I was right there with her except she served really well. I give her all the credit."

Venus Williams meanwhile used a power nap to top up her energy reserves before overcoming Davenport's spirited resistance.

Williams, the fourth seed, nodded off in the ladies locker room after rain forced the two players off Centre Court after just nine minutes and two games of their clash.

It proved to be just what the doctor ordered as Williams found an extra gear in the third set to win 6-2, 2-6, 6-1 and advance to her fourth straight semifinal at the All England Club.

Asked how she could be sufficiently relaxed to sleep in the middle of such an important match, Williams laughed and replied: "I'm low maintenance.

"I'm not a very stressed out or very hectic person. I'm an easygoing person and I just love to sleep.

"Any time I sit still I might nod off. Sometimes Serena comes by and nudges me."

On this occasion that was not necessary the ringing of a mobile phone ensuring that Williams was awake when the referee ordered a resumption of play.

Davenport, who has to have cortisone injections to be able to play with a foot injury which will require surgery later this year, afterwards sprung a surprise by revealing she was thinking about quitting the game at the end of this year.

Davenport is committed to playing until the end of the year and said any decision on whether to retire would likely be influenced by how her foot stands up to the hardcourt season in North America this summer and how successful surgery planned for early November proves to be.