Jankovic, the No. 1 seed after receiving a wild-card invitation, broke open a tight match with a late first-set break and then ran away with a 6-4, 6-0 win over No. 6-seeded Lourdes Dominguez Lino.
Jankovic ended up with the break in each set but allowed Dominguez-Lino to win just 12 points -- five on serve -- in the second set.
Fifth-seeded Lucie Safarova claimed a 7-6 (7-5), 3-6, 6-4 win over Polona Hercog despite not recording a break until the third set. No. 7-seeded Simona Halep topped Galina Voskoboeva 6-4, 6-1 and wild-card entrant Andrea Petkovic ousted eighth-seeded Annika Beck 4-6, 6-3, 7-5 in 2 1/2 hours.
Jankovic and Petkovic meet in one of Friday's semifinals. Petkovic has a 3-2 series edge versus Jankovic. Safarova and Halep will be playing for the second time. Safarova won their first match.