Defending champion Victoria Azarenka survived a huge scare before edging past American Jamie Hampton into round four.
Serena Williams also triumphed against Ayumi Morita, while Roger Federer plays Bernard Tomic in the late session.
Rod Laver Arena
Victoria Azarenka (Blr) [1] beats Jamie Hampton (US) 6-4 4-6 6-2
The Belarusian world number one showed signs of mental fragility at crucial times but came back from a break down in the deciding set to beat the 63rd-ranked Hampton.
The big-hitting Hampton struggled with back pain but led 2-1 in the third before Azarenka won five straight games to triumph in two hours nine minutes.
"She played incredibly," Azarenka said of her opponent. "She went for every single shot. She has a great future in front of her.
"She took a medical time-out but she was ripping winners all over. I thought 'can I have a back problem?!' I was feeling great but missing every shot.
"I don't think it was the best performance, honestly, today; but in another way I can say I can play better, so that's a positive note from there."
Azarenka will next play Russia's Elena Vesnina or Italian Roberta Vinci.
Serena Williams (US) [3] beat Ayumi Morita (Jpn) 6-1 6-3
Five-time champion Serena Williams was in imperious form despite needing to recover from 0-3 down in the second set to win in 66 minutes.
In the process the American set the fastest speed for a serve so far this tournament with a thunderbolt of 207kph (128.7mph) - well clear of Sabine Lisicki's next best effort of 194kph (120.6mph).
Williams, who won last year's Wimbledon and US Open titles, will next meet 14th-seeded Russian Maria Kirilenko.
Ricardas Berankis (Ltu) v Andy Murray (GB) [3]
Bernard Tomic (Aus) v Roger Federer (Sui) [2]
Casey Dellacqua (Aus) / John-Patrick Smith (Aus) v Andrea Hlavackova (Cze) [7] / Daniele Bracciali (Ita) [7]
Hisense Arena
Maria Kirilenko (Rus) [14] beat Yanina Wickmayer (Bel) [20] 7-6 6-3
Juan Martin Del Potro (Arg) [6] v Jeremy Chardy (Fra)
Caroline Wozniacki (Den) [10] v Lesia Tsurenko (Ukr)
Gilles Simon (Fra) [14] v Gael Monfils (Fra)
Goran Ivanisevic (Cro)/Cedric Pioline (Fra) v Guy Forget (Fra)/Henri Leconte (Fra)
Margaret Court Arena
Todd Woodbridge (Aus)/Mark Woodforde (Aus) v Mansour Bahrami (Iri)/Wayne Ferreira (Rsa)
Elena Vesnina (Rus) v Roberta Vinci (Ita) [16]
Jo-Wilfried Tsonga (Fra) [7] v Blaz Kavcic (Slo)
Serena Williams (US) [12] / Venus Williams (US) [12] v Vera Dushevina (Rus) / Olga Govortsova (Blr)
Cara Black (Zim) / Anastasia Rodionova (Aus) v Shuko Aoyama (Jpn) / Irina Falconi (US)
Britwatch
Sloane Stephens (US) [29] v Laura Robson (GB)
Harriet Dart (GB) v Anett Kontaveit (Est) [10]
Robin Haase (Ned)/Igor Sijsling (Ned) beat Jonathan Marray (GB)/Andre Sa (Bra) [16] 6-4 7-6
culled from: bbc.co.uk/sports
