Switzerland's Roger Federer and Russia's Maria Sharapova are top seeds at the Australian Open, with organizers sticking to the world rankings.

Federer, the defending champion, is aiming for his 10th Grand Slam singles title and has been atop the men's rankings since February 2004.

Maria Sharapova is the top women's seed at this year's Australian Open.
(Clive Brunskill/Getty Images)

Sharapova moved to the top of the women's seedings list at Melbourne Park after No. 1-ranked Justine Henin-Hardenne of Beelgium withdrew from the tournament due to personal reasons.

Sharapova has only been seeded No. 1 once, when she won last year's U.S. Open.

"I don't see it as putting any extra pressure on me," Sharapova said. "Whatever you are seeded, you've just got to go out and play your matches."

Defending Australian Open and Wimbledon champion Amelie Mauresmo was seeded second.

On the men's side, French Open champion Rafael Nadal was seeded No. 2 and is expected to recover from a groin strain that forced the Spaniard out of a warmup tournament in Sydney this week.

Nadal, who missed the last Australian Open because of a foot injury, beat Federer in four finals last year. Federer was 90-1 against all other rivals.

Every man in the Top 20 has entered the tournament, while 18 of the Top 20 women are expected to be in the draw.

The draw will be held Friday.