Defending champion Naomi Osaka on Wednesday registered an impressive straight-sets victory over Zheng Saisai of China to advance to the third round of the Australian Open.

Osaka, the No.3 seed was twice down a service break before turning on a four-game barrage to progress 6-2, 6-4 at the Margaret Court Arena.

The former World No.1 is yet to drop a set at this year's tournament, and backed up a decisive win over Marie Bouzkova on Monday with a similarly straight-forward victory over Saisai in 80 minutes.

In total, Osaka struck 20 winners and 30 unforced errors and broke serve six times, winning over half of her points played on return and allowing Saisai just five points on her second serve.

"I think I got that all out after my experience at the US Open," Osaka said when asked about being a defending champion at a Grand Slam tournament. 

"I just think of it as a new tournament. The only thing that may have changed is that people might want to beat me more. I didn't deal with that well after this tournament last year, I'll tell you. Now I think of it as a nice challenge. Someone wanting to play their best against me is something I have to feel fortunate about, because it's how I get better," she added.