Women's top seed Agnieszka Radwanska and former world number one Caroline Wozniacki suffered shock second-round exits at the Apia International in Sydney.
Flamboyant American qualifier Bethanie Mattek-Sands stunned Radwanska, the world number five, with a 7-5 6-2 win in an hour and 32 minutes, breaking in seven of the Pole's 10 service games.
Wozniacki, who had to dig deep to see off Germany's Julia Goerges in round one, was edged out by Lucie Safarova in two close sets.
The Czech broke twice in winning the first set 6-4 and took the second 9/7 in a tie-break to set up a clash with compatriot and second seed Petra Kvitova. The 2011 Wimbledon champion dropped only one game as she beat American Christina McHale in an hour.
Third seed Sara Errani and fifth seed Angelique Kerber also progressed with straight-sets wins over Lauren Davis and Kaia Kanepi respectively. Madison Keys, Tsvetana Pironkova and Carla Suarez Navarro were the day's other winners.
In the men's first round, Bernard Tomic delighted the home crowd by beating Marcel Granollers 6-3 6-0.
The 21-year-old Australian broke five times on his way to a one-sided win over a Spanish opponent ranked 16 places above him at 36th in the world.
Croatia's Marin Cilic was the only other seed in action and he came from a set down to beat German qualifier Jan-Lennard Struff 3-6 6-3 6-3.
The home wild cards in action acquitted themselves well, with Marinko Matosevic beating Florian Mayer 6-2 4-6 6-3 while Samuel Groth pushed Radek Stepanek beyond two hours before the Czech veteran eventually prevailed 6-7 (6/8) 7-6 (7/5) 6-2.
Slovenian qualifier Blaz Kavcic beat experienced Finn Jarkko Nieminen 6-4 6-3 while Albert Ramos edged out American Sam Querrey 4-6 6-3 6-4.
Nicolas Mahut and Sergiy Stakhovsky won and Alexandr Dolgopolov advanced when opponent Edouard Roger-Vasselin withdrew having lost the first set.