Australian Open: Day 6 in Melbourne

It was business as usual as Djokovic and the Williams sisters advanced in the Australian Open.(AP/AFP Photos)

The Serb world number one beat the 31st seeded Verdasco 7-6 (10/8), 6-3, 6-4 in 2hr 21min and will play Luxembourg's Gilles Muller for a place in the quarter-final.

Defending champion Stan Wawrinka reached the fourth round of the Australian Open with a straight sets win over Finland's Jarkko Nieminen

Japan's fifth seed Kei Nishikori beat American Steve Johnson in four sets to reach the last 16 of the Australian Open

Victoria Azarenka downed Czech Barbora Zahlavova Strycova 6-4, 6-4 to set up a fourth round meeting with last year's finalist Dominika Cibulkova, seeded 11.

Radwanska has rattled through her opponents at this year's tournament, with American Varvara Lepchenko her third consecutive victim to taste the dreaded 6-0 "bagel" in their third round match.

Venus Williams came from a set down to win her third round Australian Open singles match.