The Australian Open has lost its 15th seed with Dominika Cibulkova exiting after a shock loss to a qualifier.
The Czech star went down in straight sets in the second round - losing 7-6 (8-6) 6-4 to little-known Russian Valeria Savinykh.
However fifth seed Angelique Kerber fared better, moving easily into the third round.
Kerber disposed of Czech Lucie Hradecka, the German winning 6-3 6-1.
Kerber has had her best year by far on tour, winning titles in Paris and Copenhagen and reaching the Wimbledon semi-finals and the French Open quarter-finals.
She will play the winner of the clash between American Madison Keys and 30th-seed Austrian Tamira Paszek for a fourth-round berth.
Despite her rise up the rankings, she was cagey about her prospects, although strongly hinted she expected to move deep into the tournament.
'I just look from round to round,' Kerber said. 'I think the second week will be a good thing but, I mean, it's the first grand slam and every player plays very well.
'I will just give my best, and we will see how far we will go.'
Kerber said she was prepared for a hard match and, with a hotter day, was happy not to encounter a lot of resistance.
'It was very hot today and she's a tough opponent - you need to be ready for the whole match, because she's playing the ball very hard and deep in the court,' Kerber said.
'So I was just trying to move very good and just play my game. I'm happy that I won the match in two sets.