Two former world women's No.1s will fight for their lives at the quarter-final stage of the Australian Open on Wednesday.

Kim Clijsters and Martina Hingis, who have both slid down the rankings because of injury, do battle in a quarter-final with the Belgian set to bid goodbye to the Open should Hingis beat her on Wednesday afternoon.

Clijsters will retire from tennis at the end of the year and is seeking to win her first Australian Open title at her final attempt.

For Hingis, who has fought back from three years sidelined through injury to be sixth seed in Melbourne, she is aiming to make her first grand slam semi-final since the 2002 Australian Open.

The pair met at the same stage of last year's tournament, with Clijsters winning the match.

And bookmakers agree the fourth seeded Belgian is the one to beat, making her favourite to win the women's singles crown this year after her unbeaten start to 2007.

But Clijsters is well aware that her great form throughout the tournament counts for nothing if she doesn't fire against the Swiss.

"It's always nice if you beat a player in the Australian Open before, but that doesn't promise me anything," Clijsters said.

Their clash will steal some of the limelight on Wednesday from soon-to-be world No.1 Maria Sharapova, who is rated second favourite for the tournament behind Clijsters.

Sharapova's progression to the fourth round guaranteed the Russian would knock Justine Henin-Hardenne off the top of the world rankings next week, regardless of her quarter-final result against fellow Russian Anna Chakvetadze.

"It's not that big of a deal," said Sharapova, who has already had two stints at No.1.

"It means that I showed some pretty decent results last year with the help of Justine's withdrawal here and Amelie (Mauresmo) losing the other day.

"It's a good fact, but it's not something I go onto the court thinking about."

In the remaining men's quarter-finals, second seed Rafael Nadal clashes with 10th seed Fernando Gonzalez of Chile on Wednesday, while third seed Nikolay Davydenko and 12th seed Tommy Haas play on Wednesday.

On Tuesday night world No.1 Roger Federer set up a dream semi-final against Andy Roddick with a minimum of fuss, beating seventh seed Tommy Robredo 6-3 7-6 (7-2) 7-5.

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