Serena, Novak march on

Novak Djokovic underlined his supremacy in men's tennis on Friday as he marched unstoppably into the Australian Open fourth round -- along with Serena Williams, who raced through in just 44 minutes.

As Roger Federer reached a landmark 300th Grand Slam win, Djokovic still looked like the man to beat as he weathered a strong challenge from Andreas Seppi to reach the first weekend without dropping a set.

The top seed and defending champion saved two third-set points against Seppi before reeling off the next four points to clinch it 6-1, 7-5, 7-6 (8/6), his 33rd straight victory over Italian opposition.

Federer earlier went through 6-4, 3-6, 6-1, 6-4 against Grigor "Baby Fed" Dimitrov, a man whose game is so similar to his own that he admitted it was like playing a mirror.

It wasn't all plain-sailing for Federer, but with the win he became the first man to reach 300 Grand Slam victories and lies six away from Martina Navratilova's record of 306.

Maria Sharapova also weathered a fightback when she beat pint-sized American Lauren Davis 6-1, 6-7 (5/7), 6-0, helped by a strategic break and change of dress, for her 600th career win.

Williams had no such problems as she crushed overawed Russian teenager Daria Kasatkina 6-1, 6-1 in 44 minutes, the shortest match of the tournament so far.