Halep, the No. 7 seed, eliminated Errani 6-2, 6-0 in 52 minutes. Halep won two-thirds of the points on the day, including 60 percent off Errani's serve. She saved all three break points she faced while going 5-of-7 in her own break opportunities.
Jankovic, at 75 minutes the longest match of the round, lost her serve twice but also had six breaks in eight receiving games.
No. 6-seeded Angelique Kerber needed only 50 minutes to dispatch Petra Cetkovska 6-1, 6-0. The one game she lost came on a service break but she won almost three-quarters of the points off Cetkovska's serve.
Kerber goes against Jankovic in the first semifinal Saturday. They have split their first two career meetings, with Jankovic taking a 6-7 (10-12), 6-3, 6-1 decision this year in Brisbane, Australia. Radwanska won the first three times she played Halep, but Halep beat Radwanska in Rome last year in the most recent pairing.