Halep has top spot in her sights with Cincinnati win

Former number one Caroline Wozniacki and ex-number two Svetlana Kuznetsova also reached the last eight.

Sixth seed Wozniacki of Denmark stopped the impressive run of 21-year-old Australian qualifier Ashleigh Barty 6-4 6-2 to reach the tournament's quarter-finals for the fourth time.

Eighth-seeded Kuznetsova of Russia joined them in the last eight by beating Spain's Carla Suarez Navarro 6-2 6-4.

Halep reached the last eight in Cincinnati for the fifth straight year, contesting the final in 2015 and the semi-finals last year in the hard court run-up to the U.S. Open.

She can leapfrog Karolina Pliskova as world number one by winning the title claimed last year by the Czech, who was taking on Italian Carla Giorgi later on Thursday.

Halep trailed 4-2 in the opening set against Latvia's 15th-seeded Sevastova, who was aiming to take a set off the Romanian for the first time in their last four meetings.

But Halep reeled off the last four games to take the set, helped by Sevastova's unforced errors on crucial points, and won the first three games of the third set on her way to victory.

"The match felt quite tough, it was not easy at all," Halep said. "I won against the 15th player in the world playing not as I want. It's a big thing, and I'm really happy about it."