World number two Aryna Sabalenka is through to the Australian Open third round but third seed Garbine Muguruza suffered an early exit in Melbourne.
Belarusian Sabalenka, 23, had to come from behind to defeat China's Xinyu Wang 1-6 6-4 6-2.
Spain's two-time Grand Slam winner Muguruza fell in straight sets to France's Alize Cornet, losing 6-3 6-3.
Elsewhere, Polish seventh seed Iga Swiatek safely progressed while sixth seed Anett Kontaveit was knocked out.
Swiatek, 20, reached round three with a 6-2 6-2 victory against Sweden's Rebecca Peterson.
However Estonia's Kontaveit lost 6-2 6-4 to Denmark 19-year-old Clara Tauson, who claimed her first win over a top-10 opponent.