Novak Djokovic battled to a 6-7 (6) 6-2 6-4 7-6 (6) victory over Alexander Zverev and next faces remarkable qualifier Aslan Karatsev, who took full advantage of Grigor Dimitrov being hampered by a back spasm.
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Don't give up the day job
The most stressful moment of Osaka's day came when she decided to show her artistic side when signing the camera lens. It did not quite go to plan.
"I wasn't going to do anything but I saw everyone else writing cool things," she said. "I was like, 'This is my chance to hopefully draw something cute'. Then it turned out ugly. And you can't even tell what it is. So, yeah, it's a cat."
Women: Simona Halep (2)
Men: Alexander Zverev (6), Grigor Dimitrov (18)
Who's up next?
In the men's doubles, British duo Jamie Murray and Joe Salisbury are both in action with their respective partners, while wheelchair star Alfie Hewett goes for his first Australian Open singles title.