Serena Williams has claimed that she cannot afford to underestimate Dominika Cibulkova when the two meet in the Australian Open quarter-finals.
The top seed was forced to come from behind to beat Garbine Muguruza, while Cibulkova came out on top in her own three-set victory over two-time champion Victoria Azarenka.
Cibulkova was beaten by Li Na in the 2014 final, and Williams admits that nothing but her best will be good enough when she takes on the 11th seed.
"Well, she is a really good player. I mean, to be her size, she hits so hard and she plays so well. She's just such a power, compact, great player," the world number one told reporters.
"I just have to stay focused and not underestimate her. She actually almost beat me before. I want to make sure I come ready and prepared."
Williams is bidding to win a sixth Australian Open title, but she has not managed to triumph at the first Grand Slam of the year since 2010.
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