Stuttgart: Simona Halep of Romania and Caroline Wozniacki of Denmark will meet in the semi-finals of the Porsche Grand Prix after winning their respective quarter finals on Friday.

The second-seeded Halep needed 81 minutes to defeat Sara Errani of Italy 6-4, 6-4, while the fourth-seeded Wozniacki had little trouble in defeating Carla Suarez Navarro of Spain 6-0, 6-3.

Irrespective of the result in Saturday's semifinal, Halep will move up to No. 2 when the world rankings are updated Monday following Maria Sharapova's loss to Angelique Kerber of Germany on Thursday.

Defending champion and top seed Sharapova lost 6-2, 5-7, 1-6 to Kerber in the second roundon Thursday.

Wimbledon champion Petra Kvitova also suffered a 3-6, 6-7 (2-7) loss to American Madison Brengle.

Kvitova, 25, was playing her first WTA match since February following a six-week break for exhaustion. The Czech had won both her matches at the Fed Cup against France last weekend but was error-strewn in Stuttgart.

Kvitova, seeded third, made 22 unforced errors in the first set as the far steadier Brengle broke serve once but created six break points.

Brengle let a 40-0 lead and four match points slip when she served for the match at 5-4, but she recovered to dominate the tie-break and converted her sixth match point.

"I think Madison played a solid match," said Kvitova, who made 39 winners and the same number of errors.

"She didn't miss much and it was really difficult for me because when I had the opportunity for winners I missed."