Andrea Petkovic of Germany eliminated fourth-seeded Garbine Muguruza 6-1 5-7 6-2 to reach the Qatar Open semi-finals on Thursday.
Petkovic, a former top-10 player who has dropped to world No.29, met Muguruza with a 2-0 record but both wins were before 2014 and the Spaniard has since risen to a career-high ranking of No.5.
Petkovic will next face Jelena Ostapenko of Latvia, who followed up her win over two-time Wimbledon champion Petra Kvitova by defeating Zheng Saisai of China 6-4 6-3.
Zheng knocked out Australian Open champion Angelique Kerber in the second round but struggled to match the same high standard.
The third-seeded Agnieszka Radwanska was on the brink of leaving the semi-finals bereft of any of the top four, but rallied to beat Roberta Vinci 3-6 6-2 6-3.
Radwanska's reward was a semifinal with eighth-seeded Carla Suarez Navarro, who put out Elena Vesnina of Russia 6-3 7-6 (7-3). The result ensured Suarez Navarro will return to the top-10 rankings next week.
Petkovic, a winner of six WTA titles, broke Muguruza to start the match and quickly wrapped up the first set 6-1. They were 5-5 in the second when Muguruza earned her second break and took the set.
In the deciding set, Petkovic established her supremacy by breaking in the third and fifth games. She hit just 16 unforced errors compared to Muguruza's 38.
"It was so tough; Garbine is such a talented and dangerous player who put me under pressure," Petkovic said. "I was a little lucky in the end.
"I've been playing really well the past few weeks. Everything is coming together, and I'm getting my match focus again."
