Ksenia Pervak, who had to qualify for the Brisbane International main draw, served up the first big upset of the tournament after beating no.8 seed Caroline Wozniacki 2-6 6-3 7-6 (1).
The Dane raced to take the first set in just half an hour, but couldn´t carry the momentum into set two.
Wozniacki, who is yet to win a Grand Slam, started to struggle on her serve and after Pervak levelling the score at one set all, she took a 5-3 lead in the decider, giving herself a chance to serve it out. Despite Wozniacki fighting back and forcing a tiebreak, the Kazakh player stormed to take it with 7-1.
She will now play Urszula Radwanska, who dismissed Austrian Tamira Paszek 2-6 6-0 6-2.
In other first round matches, German 4th seed Angelique Kerber overcame Anna Tatishvili of Georgia in three sets 6-2 4-6 6-2, another German Sabine Lisicki eliminated Lucie Safarova of Czech Republic 6-2 6-4, American Sloane Stephens ousted Slovak Dominika Cibulkova 6-2 6-3.