Top seed Wozniacki beat world number eight Francesca Schiavone 7-6 (7/2) 6-3 but rather than face second seed Li Na, the Dane will instead take on Cetkovska who upset the Chinese player after a marathon match was decided by a third-set tie-break.
Cetkovska has enjoyed a superb week, beating Marion Bartoli and Agnieszka Radwanska who were seeded third and fifth respectively, before taking the scalp of the world number seven.
Cetkovska claimed victory despite serving up 10 double faults and had less joy converting her break points.
However, she had more success on her first serve and, with her fifth match point, the 26-year-old claimed a 6-2 5-7 7-6 (11/9) win in two hours and 41 minutes.
This week has brought welcome respite for Wozniacki who had suffered opening-round exits in her previous two tournaments.
However, on Friday the Dane was far more consistent as she beat her third-seeded opponent in one hour 48 minutes.