America's Coco Gauff fought back from a set down to beat Romania's Sorana Cirstea 4-6 6-3 7-5 in a marathon two hours and six minutes to set up a second consecutive Slam meeting with Japan's Naomi Osaka in the last 32.

The 15-year-old American had a lucky escape in what is her Australian Open debut, demonstrating her maturity by recovering from a first set loss and a 3-0 deficit in the decider.

She went a break down in the crucial seventh game of the opening set and could not recover to force the tie-break. Unperturbed, the teenager came out all guns blazing in the second, immediately breaking the Romanian and riding the break advantage through the set to take it to a decider.

It appeared nerves and lack of experience were getting to the teen sensation as she rapidly lost the first three games, but dug deep to take the next three on the trot.

The two continued neck and neck until Gauff took advantage of a single break point at 5-5 and held out serve to take the third set 7-5.

For Gauff, it is the defending champion who awaits her in the next round after Japan's Naomi Osaka came through an emotional match to beat Saisai Zheng 6-2 6-4.

The No 3 seed let her emotions get the bettter of her, throwing and kicking her racket after being broken in the second. 

"My racquet just magically flew out of my hand," joked Osaka after the game.

"I couldn't control it, I think that's how I dealt with my frustration.

No 1 seed and home favourite, Ashleigh Barty took just over an hour to breeze past Slovenia's Polona Hercog 6-1 6-4 and give the fans something to celebrate.

"It was a bit childish," she added.

Meanwhile, Caroline Wozniacki postponed her imminent retirement recovering from 5-1 down to take the first set 7-5 and followed this up with a recovery from 0-3 down to win the second 7-5. 

The 29-year-old Dane will now face Tunisia's Ons Jabeur, who conquered British No 1 Johanna Konta in her opening match.

Last year's finalist Petra Kvitova beat Spain's Paula Badosa 7-5 7-5 and 14th seed Sofia Kenin saw off fellow American and wildcard Ann Li 6-1 6-3. 

Germany's Julia Goerges fought back from a set down to knock out Croatia's 13th seed Petra Martic 4-6 6-3 7-5 and Spain's Carla Suarez Navarro, who will soon be retiring, won her first round match against Aryna Sabalenka from Belarus 7-6 (8-6) 7-6 (8-6).