Two-time champion Victoria Azarenka is through to the third round of the Australian Open after beating eighth-seed and former world number one Caroline Wozniacki 6-4, 6-2.
Azarenka's ranking slipped late last year due to a series of injuries, meaning she was unseeded for the Australian Open and was likely to have an early meeting with a top player.
Earlier, Serena Williams weathered an early challenge from Russian Vera Zvonareva before the former world number two crumbled to lose 7-5, 6-0 in the second round.
Serena's victory came about 90 minutes after older sister Venus hammered American compatriot Lauren Davis 6-2, 6-3, while sixth-seed Agnieszka Radwanska also made short work of Sweden's Johanna Larsson in a 6-0, 6-1 victory that took 44 minutes.
Other results (selected):
4-Petra Kvitova (Czech Republic) beat Mona Barthel (Germany) 6-2 6-4
19-Alize Cornet (France) beat Denisa Allertova (Czech Republic) 6-4 6-7(2) 6-2
Madison Keys (U.S.) beat 29-Casey Dellacqua (Australia) 2-6 6-1 6-1
11-Dominika Cibulkova (Slovakia) beat Tsvetana Pironkova (Bulgaria) 6-2 6-0