Naomi Osaka conceded she had been “a bit childish” after her frustrations boiled over on Wednesday in setting up a third-round showdown with teenager Coco Gauff at the Australian Open.

The reigning champion handled the blustery Melbourne conditions to defeat China’s 42nd-ranked Zheng Saisai 6-2, 6-4.

But the 22-year-old Japanese was irritated by Zheng’s defensive play and her emotions got the better of her when the Chinese broke early in the second set.

Osaka threw her racquet to the floor, then gave it a kick for good measure. The two-time Grand Slam champion also tossed away a ball and slammed the racquet down again as she slumped to her chair, covering her head with her towel.

“My racquet just magically flew out of my hand,” Osaka said mischievously, smiling. “I couldn’t control it, I think that’s how I dealt with my frustration. It was a bit childish. I just want to play one match without throwing my racquet or kicking it. That’s all I want.”

The former world No 1, seeded third for the defence of her Melbourne title, said that Zheng’s way of playing – “slicing and dicing and getting everything” – had riled her.

“It’s really tough because you start thinking – she’s not hitting winners. I definitely got very frustrated in the second set and it’s something that I knew would happen,” Osaka added. “But I didn’t know the scale, what she would do to make me frustrated.”