Williams is preparing to defend her Australian Open title

The 26-year-old began her preparations for the defence of her Australian Open title by beating Lucie Safarova 6-0 2-6 7-5 at the Hopman Cup in Perth.

The Americans are now in prime position to reach Friday's final, having beaten India in their opening tie on Saturday.

"Of course I want to be number one and I want to win Grand Slams," said Williams, currently ranked seventh.

"I wouldn't be out there if I didn't have those goals."

To regain the world number one spot, Williams will have to overhaul Justine Henin, who will start the Australian Open as favourite having won two of the last four Grand Slams.

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"I love challenges, there's nothing better than a challenge and I'm best when I am faced with one," said Williams.

"Last year I wasn't even in the top 60 and now I'm in the top 10 and just taking it a day at a time."

Williams, whose fitness was questioned when she arrived in Australia 12 months ago, looked in excellent shape as she overcame Safarova of the Czech Republic.

The Group B tie was decided when an ailing Tomas Berdych was forced to withdraw from the mixed doubles against Williams and partner Mardy Fish, giving the United States an unbeatable 2-0 lead.