Fifth-seeded Varvara Lepchenko of the United States upset defending champion Agnieszka Radwanska 6-7 (4), 6-2, 6-2 in the Korea Open quarter-finals on Friday.
Lepchenko converted three of four break points in the third set to oust the top seed. Lepchenko has beaten Radwanska twice this year, after losing five straight.
Resurgent Maria Kirilenko of Russia also reached the semi-finals with a 6-7 (3), 6-2, 6-3 win over sixth-seeded Kaia Kanepi of Estonia. Kirilenko fell out of the top 100 this year after a knee injury kept her out of the first three months of the season.
Her first semifinal in 17 months will be against second-seeded Karolina Pliskova of the Czech Republic, who beat qualifier Nicole Gibbs of the United States 6-3, 6-4.