Unheralded Aliaksandra Sasnovich stunned American third seed Sloane Stephens 6-3 6-2 to reach the WTA Korea Open semi-finals on Friday.
The Belarusian world No.1 136 provided a chastening reality check to Stephens, who is ranked 104 places higher and won her first WTA title in Washington last month.
Sasnovich, 21, will now face Anna Karolina Schmiedlova in the semi-finals after the Slovakian second seed beat Germany’s Mona Barthel 6-4 3-6 6-1.
In the other half of the drawm, Romanian top seed Irina Begu, ranked 29 in the world, defeated Swedish veteran Johanna Larsson 6-4 7-5.
Belgium’s Alison Van Uytvanck, seeded eighth, needed three sets to beat Elizaveta Kulichkova of Russia 6-1 4-6 6-2 and set up a semi with Begu.