Sizzling Serena joins sister Venus in Open last 16

MELBOURNE: World number one Serena Williams took time to wake up before sizzling into the Australian Open fourth round on Saturday, joining resurgent sister Venus and the dangerous Agnieszka Radwanska.

The American top seed, vying for a sixth Australian title and the first since 2010, was slow to get in the groove against 26th ranked Ukrainian Elina Svitolina, going down 6-4 in the first set.

But she shook off the cobwebs under the blazing sun on Rod Laver Arena to rattle through the next two sets 6-2, 6-0.

It keeps alive her quest to add a 19th Grand Slam title, which would take her to clear second on the all-time Open Era Grand Slam winners list.

She currently has 18 alongside Chris Evert and Martina Navratilova and is four behind German great Steffi Graf´s 22.

Fellow world number one Novak Djokovic and defending champion Stan Wawrinka play later Saturday, with the Serb´s chances of a fifth Australian crown improving after Roger Federer´s shock exit on Friday.

Women´s fourth seed Petra Kvitova, two-time champion Victoria Azarenka and men´s fifth seed Kei Nishikori are also in action, while eighth seeded Canadian Milos Raonic swept aside Germany´s Benjamin Becker in straight sets.

It was a day to remember for the Williams clan with Venus making the second week of a Grand Slam for the first time since Wimbledon 2011.

The evergreen 34-year-old battled back from behind to defeat Camila Giorgi of Italy 4-6, 7-6 (7/3), 6-1 and set up a fourth round clash with Radwanska.

Poland´s Radwanska defeated American Varvara Lepchenko 6-0, 7-5 and has doled out a dreaded 6-0 "bagel" to each of her three opponents at Melbourne Park this year, lurking as a dangerous dark horse.

Serena will next face Spain´s Garbine Muguruza, who overcame a mid-match stumble to beat Switzerland´s Timea Bacsinszky 6-3, 4-6, 6-0.

The 24th seed beat Serena at the French Open last year and said she was up for the challenge again in Melbourne. (AFP)