Second-seeded Caroline Wozniacki has pulled off the unlikeliest of comeback wins to beat unknown Jana Fett in the second round of the Australian Open in Melbourne.

Down 5-1 in the third set and facing a 0-30 hole, Wozniacki dug deep and rattled off 6 straight games - winning a remarkable 23 of the final 30 points of the match - to defeat her opponent 3-6, 6-2, 7-5.

Fett held match points but after looking almost certain of victory, her serve abandoned her and Wozniacki continued to fight.

Fett is ranked 119th and was making her first appearance in the main singles draw of a Grand Slam tournament.

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Wozniacki twice broke Fett's service while the Croatian player was serving for the match, including the two match points in the seventh game.

Wozniacki then broke Fett's service in the 11th game, helped by a Fett double-fault on break point and an unforced error by the Croatian which ended a 26-point rally.

She then held serve, clinching it on her first match point when Fett netted a backhand, giving her a six-game winning streak to end the match.

Wozniacki, who lost in the final of the ASB Classic in Auckland earlier this month, will now face the winner of the Kiki Bertens and Nicole Gibbs game that is set to take place this afternoon.

The Danish star wasn't the only big name requiring a stunning comeback to advance, with men's 15th seed Jo-Wilfried Tsonga just edging past promising Canadian teenager Denis Shapovalov in a five-set epic.

Tsonga was down two sets to one against the talented teenager, but battled back to win a fourth set tiebreaker to send it to a deciding set.

There, Shapovalov led 5-3, and was serving for the set, but Tsonga stormed back, breaking Shapovalov twice to seal the hard-fought win, 6-3, 3-6, 6-1, 6-7, 7-5.