The Belarusian, champion in 2012 and 2013, beat Danka Kovinic of Montenegro 6-1 6-2 and will next face unseeded Japanese teenager Naomi Osaka.

Third seed Garbine Muguruza beat Kirsten Flipkens of Belgium 6-4 6-2.

Tenth seed John Isner and 23rd seed Gael Monfils were early winners on day four in the men's draw.

Murray knocks out flatmate Marray

Jamie Murray set aside domestic loyalties to make progress in the doubles alongside Brazil's Bruno Soares.

The pair, seeded seventh after winning the build-up tournament in Sydney, beat Britain's Jonathan Marray and Aisam-Ul-Haq Qureshi of Pakistan 6-3 6-4.

Murray and Marray have been sharing a flat in Melbourne, along with fellow British Davis Cup player Colin Fleming.

"I think I'm partly to blame for jinxing it as the morning of the draw I said 'I hope we don't get a derby match in the flat,'" Fleming told BBC Radio 5 live. "But we've all played enough matches to get on and be professional.

"Jamie and Bruno look very composed coming off the back of winning in Sydney and will have high hopes here."

(BBC)