Ivanovic won 57 percent of the points on serve and 59 percent of those when receiving in a 6-3, 6-1 decision over Klara Zakopalova. Ivanovic won barely half the points when serving in the second set but finished with four of her overall six breaks.
No 5-seed Simona Halep advanced when, after Halep won the first set 6-2, Magdalena Rybarikova retired. Seventh-seeded Samantha Stosur finished off six of her seven break opportunities in a 6-4, 6-1 win over Alize Cornet.
Also Thursday, Daniela Hantuchova got past Vesna Dolonc 3-6, 6-4, 6-4 in a match that took 2 hours, 41 minutes.
Hantuchova takes on Anastasia Pavlyuchenkova and Halep goes against Alisa Kleybanova in quarterfinals in the top of the draw while Ivanovic meets Stosur and second-seeded Roberta Vinci plays No. 8-seeded Svetlana Kuznetsova in the other matches Friday.