The Williams sisters piled into the fourth round of the Australian Open on Saturday, with elder sibling Venus leading the charge with a 4-6, 7-6 (7-3), 6-1 fightback against Italian Camila Giorgi.

Williams, 34, who was diagnosed several years ago with an immune system disorder which can rob her of strength and forced her onto a special diet, recovered nicely after trailing a set and a break to finally book the win.

The 2003 Melbourne runner-up is into the second week of a grand slam for the fist time since 2011 at Wimbledon. She lost in the first round a year ago.

"I always believe in my ability, but sometimes you don't get results for whichever reason,"said the winner of seven majors. "As long as I know that I've got it in me, that's it.

"I've won big, it's not like I haven't done it before. I like to win titles, whether at a smaller event or a big event. That's what I play for.

"It's great to be in the second week. But was the fourth round my goal when I come to these tournaments? No."

Top seed Serena also had to make up ground to overturn the scoreline and defeat Elina Svitolina of the Ukraine 4-6, 6-2, 6-0.

Williams hammered nine aces and 45 winners and broke eight time.

Sixth seed Agnieszka Radwanska beat American Varvara Lepchenko 6-0, 7-5. "I really had to play my best tennis to beat her. I started well & she started playing better. Winning in two sets is important," said the Pole.

2014 finalist Dominika Cibulkova advanced over Alize Cornet of France 7-5, 6-2 while Spain's Garbine Muguruza beat Timea Bacsinszky 6-3, 4-6, 6-0 with the Swiss playing in the third round of a Grand Slam for only the second time in her career.

In the men's draw, Canadian eighth seed Milos Raonic reached the fourth round with a defeat of German Benjamin Becker 6-4, 6-3, 6-3, with the winner producing 22 aces.