German qualifier Laura Siegemund upset fourth-seeded Simona Halep 6-1, 6-2 to reach the quarterfinals of the Porsche Grand Prix on Thursday.

Siegemund is set to improve on her career-high No. 71 ranking at the indoor clay-court tournament. She equaled her previous best result of making the quarterfinals at the clay event in Charleston this month.

Halep finished 2015 as No. 2 in the world but the Romanian has dropped to No. 6 and will fall further after the latest loss.

Also, fifth-seeded Petra Kvitova of the Czech Republic rallied to beat Monica Niculescu of Romania 2-6, 7-6 (5), 6-2, and No. 7 Carla Suarez Navarro defeated wild card Anna-Lena Friedsam of Germany 6-2, 6-2.