MELBOURNE: Novak Djokovic reached the Australian Open fourth round without dropping serve Friday and Maria Sharapova was also a class apart as she floored seven-time major-winner Venus Williams.

As the sports world digested cyclist Lance Armstrong's doping confession, Djokovic won an entertaining clash with Czech crowd-pleaser Radek Stepanek to move towards the tournament's first title hat-trick since the 1960s.

And Sharapova turned day five's showpiece into a disappointment for Williams with a remorseless 6-1, 6-3 win, which briefly threatened to be her third 'double bagel' 6-0, 6-0 victory of the tournament.

Polish fourth seed Agnieszka Radwanska also reached round four without dropping a set, and there were wins for China's Li Na and former world number one Ana Ivanovic.

As baking temperatures which tested players on Thursday subsided, Djokovic, the world number one, found time to play some exhibition-style points with Stepanek but still kept enough focus to win 6-4, 6-3, 7-5.

In reaching the fourth round, the Serb has won all 43 of his service games and faced just five break points, remaining the favourite as he bids to become the first man in the Open era to win the title three times in a row.

Stepanek skipped around the court, headed the ball, used his racquet as a machine-gun and showed his behind to Djokovic as he played to the crowd at Rod Laver Arena.

Sharapova had opened her tournament with two 'double bagel' wins, and she threatened to embarrass Williams with her third before finally concededing her first game of the year for 4-1 in the first.

But there was no revival for Williams, who is returning from long-term illness, and Sharapova was able to match Steffi Graf's 1989 tournament record of reaching the fourth round for the loss of only four games.

“Well, I was a really determined player out there because I knew the tennis that she's capable of producing and playing,” said the Russian world number two.

“Despite what she's ranked or seeded, it doesn't matter when you go out on the court. She's been there. She's experienced enough to know no matter if you're playing the third round, the quarters, or the final, you have to be ready.”

Elsewhere, Poland's Radwanska schooled Britain's Heather Watson 6-3, 6-1 to make it 12 wins in a row this year, and German fifth seed Angelique Kerber beat Madison Keys of the United States.

Germany's Julia Goerges ousted Zheng Jie but fellow Chinese Li Na, the 2011 French Open champion, beat Sorana Cirstea to reach the fourth round for the fourth year in a row.

“I really want to be top three,” said Li, the world number six. “This is the goal for whole team.”

In the men's draw, Czech fifth seed Tomas Berdych, Japan's Kei Nishikori, Janko Tipsarevic and Nicolas Almagro all went through, while South Africa's Kevin Anderson upset former semi-finalist Fernando Verdasco.