"I played almost without a mistake. She had a lot of chances, but I stepped up and I was really playing my game and making so few unforced errors.
"I feel very confident going on to the next round."
The opening rally was arguably the best of the match, before Ivanovic broke Cetkovska in the second game and never looked back.
Relying on her sharp forehand, the Serb took the opening set in 24 minutes and stayed focused in the second.
|"I feel very confident going on to the next round."|
It looked like Cetkovska would possibly win a game but Ivanovic showed no mercy, hammering her opponent with powerful, flat shots from the baseline.
Cetkovska, who had not dropped a set in her first three matches, managed a total of 30 points, 16 of them from Ivanovic's unforced errors.
The Australian Open runner-up will again be the favourite in her quarter-final match, having beaten Srebotnik in all their four meetings, including a straightforward win in Melbourne in the third round.
The Serb has lost four times to Schnyder but prevailed in their last three meetings, twice on clay.
Later, third seed Jelena Jankovic, also of Serbia, reached the quarter-finals by defeating Agnieszka Radwanska of Poland 6-3, 7-6.
Jankovic will play qualifier Carla Suarez Navarro for a place in the semi-finals after the Spaniard defeated Italy's Flavia Pennetta 6-3, 6-2 to reach the last eight.