Halep claimed her first tournament title at last week's event in Germany and kept the chances for a second alive with a 6-3, 6-1 win over Lesia Tsurenko. Halep dropped just one game in eliminating top-seed Roberta Vinci in the second round.
Halep fought off all three break chances Tsurenko set up and cashed in four of her seven break opportunities.
Qualifier Garbine Muguruza ousted second-seeded Dominika Cibulkova 6-4, 6-4. She kept ahead by saving six break points in the first set and had a pair of second-set breaks in gaining a spot in the semifinals.
There she'll go against fourth-seeded Kirsten Flipkens, who got by No. 7-seeded Urszula Radwanska by the same 6-4, 6-4 score. Flipkens had breaks in half of Radwanska's games serving.
Kate Middleton recycles dress at movie premiere
Jordana Brewster on Paul Walker: 'He was an enormous presence in my life'