Tennis: Super Serena, Djokovic soar into Aussie fourth round

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.

It was a moment that once again demonstrated the mental strength of the Serbian 10-time Grand Slam winner -- against an awkward opponent who beat Federer at the same stage last year.

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.

"It's very exciting, I must tell you," said the Swiss, who also became the oldest man to reach the round of 16 since Andre Agassi in 2005.

"Not something I ever aimed for or looked for, but when it happens, it's very special."

- Dress for success -

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.

Sharapova left the court after she lost the second-set tiebreak but after she came back refreshed and revitalised, she raced to victory to set up a clash with Switzerland's Belinda Bencic.

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.

"I definitely think I played better today. Everything I've been trying to work on was kind of clicking today," said the buoyant world number one, who is seeking a record-equalling 22nd Grand Slam title.

The busy day of action helped take the focus off corruption claims which have overshadowed the year's first Grand Slam after a report said players had been suspected of fixing matches but never faced action.

Belgium's David Goffin awaits Federer in round four, after he beat Dominic Thiem 6-1, 3-6, 7-6 (7/2), 7-5 in a match which included a generous act of sportsmanship from the Austrian.

Thiem, leading in the second set, told the umpire to give a point to Goffin rather than replay it after a Hawk-Eye challenge found a shot from the Belgian had landed in.

Elsewhere, fourth seed Agnieszka Radwanska reeled off nine straight games to floor Monica Puig 6-4, 6-0, despite continuing pain from a left-leg injury which stopped her competing in Sydney last week.

And Roberta Vinci was knocked out by Germany's Anna-Lena Friedsam in three sets, meaning there will be no rematch of last year's US Open semi-final when she halted Williams' bid for a calendar-year Grand Slam.