Venus Williams calls her outfit an 'illusion', not to worry.

THE ASSOCIATED PRESS

MELBOURNE, Australia -- Being a tennis player in the age of Twitter and Facebook means Venus Williams can communicate with fans like never before.

This explains the recent tweet about her underwear.

The bright yellow mini-dress that Williams wore Saturday in her third-round win at the Australian Open -- and all earlier rounds -- has raised eyebrows. Its plunging V-neck and cabaret-style slits up the front prompted fans, bloggers and reporters to question if there was anything underneath.

"The whole idea is about an illusion," Williams said after defeating Australia's Casey Dellacqua, 6-1, 7-6 (4) to reach the fourth round. "Obviously the most effective part of the illusion are the slits."

Two days earlier, the seven-time Grand Slam champion tweeted on the subject to her 438,000 Twitter followers:

"My dress for the Australian Open has been one of my best designs ever! Its all about the slits and V-Neck," she tweeted, and followed up with this reassurance: "I am wearing undershorts the same colour as my skin, so it gives the slits in my dress the full effect!"

The No. 6-seeded Williams, who designs two sportswear labels, sketched out the dress herself.

"This is completely my design," she said, describing her style as fashion forward but also classical. "Anything I wear on the court probably you could wear 20 years from now."

Like most top players, Williams uses social networking sites to touch base with fans. She says she spends more time online when not competing and insists she posts her own updates.

"I've always been a really private person. So I do try to keep a part of my life private," she said, but added that she enjoys the interaction with fans. Williams said she doesn't follow news while playing a tournament but gleaned from word-of-mouth there was chatter about her dress.

Whistles rang out from the stands at the packed Rod Laver Arena midway through Saturday's match when the wind blew up Williams' skirt in a Marilyn Monroe moment.

Williams cruised through the first set but was tested in the second, which she started with a 4-2 lead.

The No. 980-ranked Dellacqua held serve in the next game and then broke Williams in the next, when the American double-faulted on the last point to level the score to 4-4.

Dellacqua held in the next game to take a 5-4 lead, aided by a trio of errors from Williams, playing for her 10th time at the Australian Open, where she was a runner-up in 2003.

The games went on serve for the next three to bring the score to 6-6 and force a tiebreaker, which Williams closed with an ace on her fourth match point.

Dellacqua had a career-high ranking of 39 in 2008 but didn't play most of last year while recuperating from shoulder surgery.

"It's nice knowing I can compete and hold my own with girls like that after only really hitting solid tennis balls for the last six or so weeks," said the 24-year-old Australian, who praised William' serve as one of the best in the world. "She can hit fast, slice. She can do it all ... it's a hard ball to face."

No. 17-seeded Francesca Schiavone will face Williams in the fourth round after the Italian defeated Agnieszka Radwanska 6-2, 6-2.

Williams remains on course for a semifinal meeting with her sister Serena, the defending Australian Open champion who had a 6-0, 6-3 victory over Carla Suarez Navarro.

The sisters are also the defending doubles champions at Melbourne, where they are into the quarterfinals and remain on track for collecting their 11th Grand Slam doubles trophy.

Serena shares her sister's taste for flashy on-court fashion. In Melbourne, where she is the top seed, Serena has chosen a more conservative outfit -- a golden tank dress with nearly knee-length white shorts -- but shared a word of advice when asked if she had any fashion tips.

"Whatever you wear, own it," Serena said. "Some people come out here with crazy designs but they own it. They really feel comfortable in it. I think as long as you feel comfortable in what you have and what you do, you'll be fine."