The third-seeded former champion Wozniacki handled fellow former top-ranked star Ana Ivanovic, of Serbia, 6-3, 7-5, while an eighth-seeded Jankovic upended fourth-seeded U.S. Open champ Samantha Stosur 6-4, 6-2 on the hardcourts at Dubai Tennis Stadium. The Aussie slugger Stosur was the runner- up to current world No. 1 and Australian Open champion Victoria Azarenka last week in Doha.
The top-seeded Azarenka pulled out of Dubai on Wednesday because of an ankle injury.
Wozniacki titled here a year ago by beating two-time Grand Slam champion Svetlana Kuznetsova in the final.
"I'm very pleased to get through that in straight sets," Wozniacki said after besting Ivanovic on Day 4. "Ana really stepped it up in the second set, took the balls very early, and just played really well. She took her chances and had nothing to lose."
Up next for Wozniacki will be German Julia Goerges, while Jankovic's semifinal opponent on Friday will be fifth-seeded Pole Agnieszka Radwanska. The Serbian Jankovic was a Dubai finalist back in 2005.
"I'm happy with the win," Jankovic said after beating Stosur. "It's never easy. Against her, we always have tough matches."
Wozniacki will meet Goerges for a fifth time, with the women splitting their first four encounters, while Radwanska and Jankovic will clash for a third time after splitting their first two matchups.
Thursday's other quarters saw the steady Radwanska rout ninth-seeded German Sabine Lisicki 6-2, 6-1 in 66 minutes and Goerges come back to ground Slovakian veteran Daniela Hantuchova 4-6, 6-3, 6-4. Hantuchova was a titlist in Pattaya City earlier this month.
The 2012 Dubai champ will earn $446,778.