Maria Sharapova and Serena Williams on Friday continue their collision course towards a fourth round showdown at the Australian Open.

Women's fourth seed Sharapova starts proceedings on Rod Laver Arena on Friday in a third round match against Croatian Jelena Kostanic, ranked just inside the top 100.

Williams, the 13th seed and the subject of doubts surrounding her fitness coming into the tournament, faces her toughest test so far against 17th seed Daniela Hantuchova of Slovakia in her third round encounter.

If Sharapova and Williams both win, it will set up an irresistible fourth round battle between the two.

Women's No.1 seed Lindsay Davenport, who continues to slide under the radar with a minimum of fuss, takes on Maria Kirilenko on Rod Laver Arena.

And men's No.2 seed Andy Roddick is also in action against Frenchman Julien Benneteau.

After the demise of Australia's top singles hope Lleyton Hewitt on Thursday night, the three remaining Australians in the singles will find out later on Friday when their weekend third round matches will be.

Samantha Stosur - Australia's last remaining women's singles hope - and unseeded men Peter Luczak and Nathan Healey are all through after wins on Thursday and at least two are likely to earn centre court billing at the weekend.

Hewitt wasn't as lucky on Thursday night, knocked out in four sets by Argentine Juan Ignacio Chela 6-4 6-4 6-7 (10-8) 6-2 in a match lasting more than three hours.

Hewitt, who received treatment throughout much of the third set for an ankle injury, needed five set points in the third set tie-break to push the game into a fourth set.

But Chela raced to an early 3-0 lead in the fourth after breaking Hewitt's serve in the second game and maintained the advantage despite his own fitness concerns.

Chela appeared to be battling cramp late in the match.

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