I want it bad, says Serena

"Some days it feels good and some days it gets a little cold and I get a strange feeling. I have to have pretty heavy taping on it."

Since winning the Australian Open in January, Williams's season has been blighted by injury and illness. A shoulder problem and stomach illness ruined her Spring campaign, while the fractured ankle also forced her to miss last month's French Open. She then spent four weeks resting in bid to be ready for Wimbledon.

However, despite the lack of match practice and the ongoing fitness problems, Williams still believes she is capable of recapturing the crown she first won in 2002 and then again a year later.

The American said: "I'm fighting on adrenaline. I have a lot of it. I think tennis is 60 or 70 per cent mental. I figure that I've been playing since I was four so, if I can't do it now, I'm never going to be able to play tennis.

"I definitely think I'm going to have to pick up the level of my game, though. I'm just not hitting it the way I want to and I'm not doing technical things the way I would like to.

"But I'm here to stay. I think I have the best chances of the people left in the draw. I think I'm probably the most mentally tough person out here. I feel as if I have nothing to lose and only things to gain. I want to win this title real bad."

Williams's self-confidence derives from her extraordinary record in Grand Slams and is fuelled by a hunger to end her career as one of the greats of the game. She admits to having set herself a target of Slams, but will not reveal the precise number. She added: "I have a number in my head and I will reach that number. It's definitely not single figures and definitely not seven."

To make it eight in this week, she may have to once more overcome sister-Venus. The pair, who are more accustomed to meeting in Grand Slam finals, are drawn to play one another in the fourth round.

With characteristic determination, Serena insists there will be no special treatment for her out-of-form sister, adding: "You can't feel sorry for anyone, especially at Wimbledon. It doesn't matter who you are playing.

"I was watching Tim Henman and I felt sorry for him after his defeat. But then I thought, 'Why would the other guy let him win?'

"That's obviously the attitude to have. The other guy obviously wanted to win too. When I'm out on court I feel like I have to win under any circumstances."

Venus, the 2000 and 2001 champion, has slipped down the world rankings in recent months and is only seeded 14 for the tournament. She must beat No20 seed Daniela Hantuchova tomorrow to set up the all-Williams encounter, but is already looking further ahead.

Venus said: "We're really living our dream. When we were growing up we always dreamed we would be out there together in finals. Even, in this case, it'll be really great. We always motivate each other to be at our best."