World No.1 Serena Williams has come from a set down to join older sister Venus in the round of 16 at the Australian Open.

Serena Williams, chasing a sixth crown at Melbourne Park and a first since 2010, was pushed hard by Ukraine’s Elina Svitolina before triumphing 4-6 6-2 6-0 in one hour and 39 minutes.

“She played really well,” said Williams of Svitolina, the No.26 seed.

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“She’s one to watch, she works very hard and has come a long way.

“It was a good match and she made me work really hard.”

The top seed’s reward was a fourth-round date against Spain’s No.24 seed Garbine Muguruza who beat Switzerland’s Timea Bacsinszky 6-3 4-6 6-0.

Muguruza recorded a shock straight-sets victory over Williams the last time they met in the second round of the 2014 French Open.

Venus Williams also dropped the first set on Saturday before advancing to the last 16 at a major for the first time in four years.

Williams, 34, hung tough to beat Italy’s Camila Giorgi 4-6 7-6 (7-3) 6-1 in two hours and 26 minutes, setting up a big fourth-round clash with Poland’s Agnieszka Radwanska.

The 18th-seeded Williams won the most recent of her seven major titles at Wimbledon in 2008 and until Saturday had not been through to the last 16 at a grand slam since 2011 at the All England Club.

The sixth-seeded Radwanska continued her relentless charge through the draw with a 6-0 7-5 win over American Varvara Lepchenko.

The 2012 Wimbledon runner-up has dropped just nine games in her first three matches, claiming a bagel in each, to send a clear warning to her rivals as the championship heads into a second week.

Whether or not the hiring of the legendary Martina Navratilova last month as coach is responsible for Radwanska’s new found ruthlessness, the world No.6 is in superb touch for a quarter-final qualifier on Monday.

“The most important thing is I won in two sets,” Radwanska said after reversing two previous losses to Lepchenko, the tournament’s 30th seed.

Two-time champion Victoria Azarenka‘s hot run at Melbourne Park continued, when she reached the fourth round in straight sets.

Azarenka, unseeded and ranked 44th in the world after a foot injury ruined her 2014 season, downed Barbora Zahlavova-Strycova 6-4 6-4 on Margaret Court Arena.

Azarenka saved five break points in the opening set, when she broke the Czech world No.23’s serve with the score 4-4.

– AAP