American teenager Coco Gauff came from a set down to advance to set up a third-round meeting with defending champion Naomi Osaka.

15-year-old Gauff followed up her first-round win over Venus Williams with a second-round victory over Sorana Cirstea.

The American had to come from a set down to see off her Romanian opponent and Gauff came from a break down in the final set to wrap up the match in two hours and seven minutes.

Gauff thanked the Australian support: "Honestly, I didn't think I would get so much support in Australia. I was down 3-0 and you really made me believe."

Naomi Osaka overcame her frustrations to continue the defence of her title with a 6-2 6-4 win over Saisai Zheng.

The third seed threw her racket after dropping serve early in the second set and joked after the match that her racquet "magically flew out" of her hand.

It is the second Grand Slam in a row where Gauff will play Osaka, who was also the defending champion when the pair met in the US Open third round in September.

The Japanese won 6-3 6-0 that day and the two embraced at the net after the match.