Serena struggled early on as she lost the opening set to Ukraine's Elina Svitolina, before she dropped just two games on her way to a 4-6, 6-2, 6-0 victory.

Sister Venus also had to display her fighting qualities to progress to the fourth round of a Grand Slam for the first time since Wimbledon in 2011 as she beat Italy's Camila Giorgi 4-6 7-6 (7-3) 6-1.

"I do my best every single day," she said.

"That's pretty much the way it goes, I think just not being afraid is the most important thing.

"I like to win titles, whether it's a smaller event or a big event.

"It's great to be in the second week.

"But is the fourth round my goal when I come to these tournaments? No."

Elsewhere in the women's draw, 2014 Wimbledon champion and fourth seed Petra Kvitova suffered a shock straight-sets exit at the hands of American Marian Keys.

American Marian Keys provided the shock of the day as she beat fourth seed Petra Kvitova in straight sets ©Getty Images



Belarusian Victoria Azarenka, who is a former world number one, continued her disposal of seeds as she beat Barbora Zahlavova Strycova 6-4, 6-4, while Agnieszka Radwanska and Dominika Cibulkova also booked their places in the next round with comfortable wins.

Djokovic meanwhile maintained his quest for his fifth Australian Open title as he negotiated a tricky test against Spaniard Fernando Verdasco with relative ease, despite being taken to a tie-break in the opening set.

The Serbian upped his game in the second set, demonstrating his dominance in all areas of the court to which Verdasco had no answer.

Novak Djokovic recovered from a tight first set to beat Spaniard Fernando Verdasco ©Getty Images



Djokovic eventually sealed a trouble-free 7-6 (10-8) 6-3 6-4 win and he will be joined in round four by defending champion Stanislav Warwinka, who beat Finnish star Jarkko Nieminen in straight sets.

Japanese sensation Kei Nishikori, along with Canada's Milos Raonic, Spain's Feliciano Lopez and Spain's David Ferrer all sealed their progress, with US hope Jon Isner the only seed to fall.

He lost 6-7, 4-6, 4-6 to dark horse Gilles Muller, who ousted 13th seed Roberto Batista Agut in round two.

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