U.S. Open semi-finalist Vandeweghe raced to a 5-4 lead in the opening set on the back of her strong service game. The 26-year-old then sealed a decisive break to clinch the first set and gain the upper hand in the contest.
Despite stepping up her attack, Romania's Halep struggled to find a way past her opponent who cruised through the second set to reach the last four of a claycourt event for the first time.
Vandeweghe next takes on sixth seed Caroline Garcia who later overcame Ukraine's Elina Svitolina 6-7(4) 6-4 6-2.
Anett Kontaveit emerged victorious 7-5 6-7(6) 6-4 against Anastasia Pavlyuchenkova and the Estonian next takes on fifth seed Karolina Pliskova who came from behind to beat a determined Jelena Ostapenko 5-7 7-5 6-4 in the evening session.
(Reporting by Shrivathsa Sridhar in Bengaluru; Editing by Christian Radnedge and Pritha Sarkar)
