Defending champion Serena Williams has been knocked out of the Australian Open in straight sets by Slovakian Daniela Hantuchova in the third round at Melbourne Park.

Williams, the No.13 seed, lost 6-1 7-6 (7-5) in one hour and 31 minutes and had no answer to an inspired performance from the 17th seed, who had never beaten the American in three previous meetings.

Hantuchova broke Williams' serve in the second game of the opening set and twice more after a rain interruption of more than 30 minutes when she was leading 3-1.

Tournament organisers' decision to leave Rod Laver Arena's retractable roof partially open - despite thunderstorms just two hours earlier - backfired within minutes when heavy rain forced the closure of the roof.

After the motorised roof took 15 minutes to close fully, ball boys and girls then had to mop up the court with towels for play to continue.

Hantuchova managed to pick up where she left off, though she had her nervous moments.

The Slovakian fought back from a break down in the second set and squandering four match points to seal victory in the tie-break.

It means both Williams sisters are out in the first week of the tournament after Serena's sister Venus was beaten in the first round.

Hantuchova now plays No.4 seed Maria Sharapova in the fourth round.

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