The Wimbledon women's final might be a Williams family affair, but it will not be decided by a conference around the breakfast table. Venus Williams yesterday rejected out of hand the idea - sparked unwittingly by Elena Dementieva, her defeated semi-final opponent - that she may collude with Serena, her sister, to decide in advance who wins tennis's biggest prize.

The Williams sisters eat together, train together and are sleeping under the same roof at Wimbledon, yet they will face each other across the Centre Court net tomorrow in a contest that still puzzles many of their rivals.

Dementieva, beaten 6-1, 7-6 by Venus, was forced to issue a clarification last night to say that she had not meant to suggest that a family decision may decide the outcome of a final that carries a first prize of £750,000, as well as the greatest accolade in the sport. But the cat was already out of the bag and the Williams family thought process was undergoing forensic examination.

Dementieva had probably expressed what many people already believe, that playing in the final of a grand-slam event against your sister and best friend raises all sorts of issues. “I cannot imagine playing against someone from my family,” Dementieva said. “I think it's really hard for them because they are both great players and they both deserve to win. There is only one trophy so it's a shame. But if they play the same tournaments, they have to face it sometime. I have a lot of respect for Serena and Venus. They are extremely professional in everything they do.”

There has not been an all-Williams final in a grand-slam tournament since 2003 - with Serena winning five of the six finals they have contested - yet the suspicion lingers that the sisters could not take each other on in a fair fight.

Venus, though, responded angrily to that suggestion yesterday. “I find that question offensive because I am extremely professional in everything that I do on and off the court,” she said. “I contribute my best in my sport and I also have a tonne of respect for myself and my family. It's ridiculous. Our main focus was obviously getting to the final. From there, it is every Williams for themselves.”

Dementieva was understandably disappointed that she could not crash the Williams party. The Russian went into the semi-finals as the highest-placed seed left in the tournament, but her listing at No5 counted for nothing against the big guns of Venus. Even as defending champion, Williams was seeded only seventh at the championships and she is doing her best to prove that Wimbledon's numbers do not add up. On Wimbledon's lush grass and in front of 15,000 spectators on Centre Court, she is transformed and even a player of Dementieva's quality would have needed something very special to beat her.

The omens were bad from the start: Williams allowed Dementieva only three points on the Russian's first two service games to rush into a 4-0 lead in the first set before closing it out 6-1. The crowd willed Dementieva on and she must have sensed their urging to make a game of it, matching Williams shot for shot in the second set. Once in the tie-break, though, Williams raised her game and finished off Dementieva's challenge.

Venus did a little victory jump for joy that she was in her second consecutive Wimbledon final on Centre Court tomorrow when, she says, she will face the player she respects most in the game - her sister.