Former world number one Victoria Azarenka suffered a shock defeat by American teenager Ashlyn Krueger at the Libema Open in the Netherlands.
Two-time Grand Slam champion Azarenka was stunned 6-3 6-2 by the 19-year-old.
Victory at the grass-court tournament in s'Hertogenbosch marks unseeded Krueger's first win over a top-20 player and a maiden WTA quarter-final.
In the men's draw, Italian second seed Jannik Sinner beat Kazakh Alexander Bublik to reach the last eight.
World number nine Sinner, who is looking to bounce back on grass in the run-up to next month's Wimbledon after a disappointing second-round exit at the French Open, beat Bublik 6-4 6-2 in the opening round.
Sinner, a quarter-finalist at the All England Club last year, will face Finland's Emil Ruusuvuori, ranked 42 in the world, in the next round after he edged out Frenchman Ugo Humbert 6-2 6-7 (6-8) 6-4.
Elsewhere in the women's draw, Russian top seed Veronika Kudermetova progressed to the quarter-finals with a comfortable 6-1 6-3 victory over Canadian qualifier Carol Zhao.
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