Ranked 72nd in the world, Osaka's next challenge comes in the form of Simona Halep - the Japanese joking she was feeling tired just watching the Romanian's gruelling clash with Lauren Davis.

"I was sweating more watching that match than I was with my match," said a smiling Osaka. "But, yeah, I've played her twice, and both times it was three sets.

"I had fun both times. I feel like I learned a lot. I feel playing the number one is really an honour. No matter what happens, I'll try my best. I'll just see what happens from there."

Halep and Davis equalled the record for the longest match in Australian Open women's singles history.

Top seed Halep came from a set down to prevail 4-6 6-4 15-13, the 48 games matching the previous mark reached by Chanda Rubin and Arantxa Sanchez Vicario in 1996.

Angelique Kerber prevailed against Maria Sharapova in the battle between the only two grand slam winners left in the draw, while Karolina Pliskova and Carolina Garcia also made it to the fourth round after respective wins over Lucie Safarova and Aliaksandra Sasnovich.

Pliskova will face fellow Czech Barbora Strycova, who ousted Bernarda Pera 6-2 6-2, while Garcia's next opponent is Madison Keys after the American's 6-3 6-4 success over Ana Bogdan.