Venus Williams was one of the top-ranked players to fall in Ohio.
Halep needed just 54 minutes to cruise past Sloane Stephens in the semi-finals, and can displace Karolina Pliskova as the top of the ranking with a victory over Garbine Muguruza on Sunday.
Angelique Kerber fell behind at the outset, repeatedly missed routine shots and fell to Karolina Pliskova 6-3, 6-1 in the championship match on Sunday at the Western & Southern Open.
Rafael Nadal and Karolina Pliskova got their doubleheader day started with victories at the Western & Southern Open on Friday afternoon
Karolina Pliskova swept a pair of matches with little rest in-between to reach the Western & Southern Open semifinals. Rafael Nadal couldn't do the same.