Xavier Malisse of Belgium aims towards a linesman during his match against Thomas Johansson of Sweden in Melbourne on Wednesday. Malisse lost 3-6, 6-3, 5-7, 6-4, 3-6. (Reuters)

Melbourne: Defending champion Serena Williams issued an ominous warning to her Australian Open rivals as the tournament’s big names started flexing their muscles on Wednesday.

Williams was not quite at the top of her formidable powers but was still impressive on a day when Andy Roddick, Lindsay Davenport, Maria Sharapova, Justine Henin-Hardenne and David Nalbandian all recorded impressive wins.

Williams had appeared to be struggling for fitness and form as she stumbled to a three-set victory over Li Na in the opening round but her 49-minute 6-3, 6-1 destruction of unseeded Camille Pin dispelled any concerns about her game.

“Everyone’s a threat but I’m real serious and I’m here to be a threat as well,” she told a news conference.

Williams’ main rivals in the top half of the women’s draw all made it through safely, while the bottom half of the men’s draw was opened up with the loss of three more seeds.

Robby Ginepri, Radek Stepanek and Tomas Berdych all made early exits, leaving second seed Roddick and fourth-seeded Nalbandian as favourites to meet in next week’s semi-finals.

Roddick outslugged South African serve-and-volleyer Wesley Moodie 7-5, 6-3, 6-2 to remain unbeaten this year following his win in the Kooyong Classic while Nalbandian beat improving Swiss shotmaker Stanislas Wawrinka 6-4, 3-6, 6-4, 6-2.

“There’s no such thing as an open draw,” Roddick protested. “If there’s one thing we’ve learned by seeds getting knocked out, it proves anybody can play.”

World No. 1 Lindsay Davenport booked a third-round encounter against 25th seed Maria Kirilenko with a hard-fought 7-6, 6-3 victory over Karolina Sprem. The Californian was not at her best but was able to raise her game when it mattered.

“I didn’t panick and I wasn’t uptight about anything,” Davenport said.

On a day when several leading women’s seeds scored impressive wins, 2004 champion Justine Henin-Hardenne of Belgium beat Hana Sromova 7-6, 6-1 to confirm her position as tournament favourite.

The Czech provided eighth seed Henin-Hardenne with some stubborn resistance in the opening set but her challenge faded quickly when she rolled her left ankle and crashed to the court.

Henin-Hardenne has replaced compatriot Kim Clijsters as the bookmakers’ favourite to win the title after a brilliant start to the season. She is yet to drop a set in her two matches so far but said winning was not as easy as it used to be.

“We have to be focused in every match because all these players, they want to beat us and they want to be at our place,” she said. “We need to be one hundred percent all the time. I think that's changed from a couple of years ago.”

Fourth-seeded Sharapova led a powerful group of five Russian women, including 2004 US Open champion Svetlana Kuznetsova and sixth seed Nadia Petrova, into the next round.

The former world No. 1 and 2004 Wimbledon champion showed little sign of the shoulder injury that had threatened to derail her Open chances as she ground out a 6-1, 7-5 victory over American qualifier Ashley Harkleroad.

The only women’s seeds to lose on Wednesday were number 18 Elena Likhovtseva and Jelena Jankovic, who was seeded 22nd.

Bulgarian teenager Tszvetana Pironkova crashed back to earth after her stunning upset win over former world No. 1 Venus Williams, losing 7-5 6-2 to Laura Granville.

Bogomolov fined

American Alex Bogomolov was fined $4,500 for verbal abuse and obscene language after his heated first round match with Chile’s Fernando Gonzalez.

Bogomolov beat the ninth seed 4-6, 7-6, 6-3, 6-7, 7-5 on Tuesday to set up a second-round match with Frenchman Paul-Henri Mathieu but the result was overshadowed by an ugly confrontation.

Television replays showed the pair arguing angrily during a change of ends as frustrations threatened to boil over.