Top seed Serena Williams has powered into the fourth round of the Australian Open with a straight-sets victory over Slovakia’s Daniela Hantuchova.

With players desperately seeking to spend as little time on court as possible on another oppressively hot Melbourne day, Williams won 6-3 6-3.

“It’s tough mentally and physically but I was prepared,” said the American, who has dropped only 12 games in her opening three singles matches.

The clash against Hantuchova began a tough day for the world No.1 who is also scheduled to partner her sister Venus in doubles.

Only minutes before Williams won through, German ninth seed Angelique Kerber became the first woman into the fourth round of the Open thanks to a straight-sets victory over American Alison Riske.

Kerber said she had to force herself to focus on her game and not the weather.

“I’m just happy to have won and got off the court before it became really hot,” she said.

“I was trying to concentrate on each point and forget about the sun.”

Kerber won 6-3 6-4 to reach the same point in the championship as last year.

Fourth seed and last year’s runner-up Li Na is into the fourth round, but she had to do it the hard way against Czech Lucie Safarova.

Safarova, the 26th seed, raced through the first set 6-1 against Li, and was in the ascendancy in the second before dropping it in a tie-break.

The third was a tight affair early on, but Li eventually took control and eventually won 1-6 7-6 (7-2) 6-3 in a match lasting two hours and 37 minutes.

Also through is Italy’s Flavia Pennetta.

The 28th seed accounted for Germany’s Mona Barthel 6-1 7-5, getting the job done in 74 minutes.

A top temperature of 44 degrees was forecast for Melbourne on Friday.