World number two Caroline Wozniacki was stunned by Kiki Bertens in the third round at the Madrid Open.
The Dane could have overtaken Romania’s Simona Halep as world number one by winning the tournament, but was beaten 6-2 6-2 by Dutch world number 20 Bertens in just 61 minutes.
Bertens will now face five-time Grand Slam champion Maria Sharapova.
The Russian, who dropped out of the world’s top 50 last month, beat France’s Kristina Mladenovic 6-3 6-4.
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Defending champion Halep had earlier registered a straightforward 6-1 6-4 win over Czech Kristyna Pliskova to reach the quarter-finals.
Halep barely looked troubled as she won five consecutive games to clinch the opening set in 29 minutes.
Pliskova produced a better second set but she could not maintain any pressure, with Halep saving all five of the break points she faced.
She finished with 32 unforced errors to Halep’s 13 as her opponent closed out victory in 77 minutes.
Halep will face sixth seed Karolina Pliskova – twin sister of Kristyna – after she knocked out American Sloane Stephens 6-2 6-3.