They are sisters, best friends and doubles partners, but on Friday, Venus and Serena Williams will be on opposing sides of the net in the French Open mixed doubles final.

Venus, 17, and her partner, American Justin Gimelstob, will try to win their second Grand Slam final in a row, following up on their victory at the Australian Open in January. The jocular pairing of intense big servers hasn't lost a set at the French.

"We're a good team because were both tall and we don't have to feel awkward with short partners," Williams told the IBM Roland Garros Web site with a chuckle. "He's the most hyperactive guy I've met for his age. I'm a laugher."

Serena, 16, has found a new partner in Argentine Davis Cupper Luis Lobos, and they found instant magic together, dropping only one set during their campaign to the final.

The two met when Serena challenged the friendly Lobos to a singles match at the Australian Open. The singles encounter has yet to come off, but they became fast friends.

"Serena's an excellent player, a great girl, the best mixed partner I've had," said the 27-year-old Lobos, whose added that he is stirred by Serena's athletic volleys, pounding serve and low returns.

Gimelstob, 21, is enamored by Venus' game. "Venus is the one of the best if not the best girl in the world. I play pretty good doubles and she's just a great player." Venus and Gimelstob say they are not up to their Australian Open standards yet. But Gimelstob is guaranteeing a victory in the final."I'll play great tomorrow," he said. "I anticipate an unbelievably strongperformance by myself."

Venus won't let Gimelstob take all the blame, saying she hasn't played completely up to snuff either. However, Gimelstob says in the final against Serena and Lobos, for the first time, the "Venus factor" won't come into play."

"It will be canceled out," he said. "The other girls were so intimidated by Venus that they played less than they were capable of. But Serena's not intimidated. Venus and Serena will cancel each out. Whoever plays better between Luis and I will decide the match."

Venus and Serena have played each other twice in singles (both times victories for Venus), but never in doubles or mixed. "Usually in practice we play guys and we start out singing a song, the theme song from the cartoon "Dexter's Laboratory," Venus said. "It's kind of silly. We get kind of silly"

While the finalists say that playing mixed doubles is a blast and have been frequently seen at Roland Garros laughing after taking a roll on the clay, on Friday, they promise they will be intense. "We're going to have serious game faces on from the first toss of the ball," Gimelstob said.

Venus agreed, but added that she might get the giggles. "Serena's going to laugh and then I'm going to laugh," she said. "Then Luis is going to laugh and Justin will laugh." Gimelstob countered, "I'm only going to laugh because Venus makes me laugh. It doesn't come naturally."

However, Venus did say that give the opportunity, she'll whack a sitter at Serena. "Oh, sure," she said.