German qualifier Laura Siegemund upset fourth-seeded Romanian Simona Halep 6-1 6-2 to reach the quarter-finals 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 in her hometown. She equalled 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.
Top-seeded Agnieszka Radwanska of Poland beat Andrea Petkovic of Germany 1-6 6-1 6-2.
Petkovic fell heavily at the start of the second set and never regained her game.
In the quarters, Radwanska will meet Karolina Pliskova of the Czech Republic, who beat Ana Ivanovic 6-4 6-2.
Also, fifth-seeded Petra Kvitova of the Czech Republic rallied to beat Monica Niculescu of Romania 2-6 7-6 (7-5) 6-2.
Carla Suarez Navarro defeated wildcard Anna-Lena Friedsam of Germany 6-2 6-2 and Roberta Vinci beat Julia Goerges of Germany 6-3 6-4.