SEOUL, South Korea -- Fifth-seeded Varvara Lepchenko of the United States upset defending champion Agnieszka Radwanska 6-7 (4), 6-2, 6-2 in the Korea Open quarterfinals 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 semifinals with a 6-7 (3), 6-2, 6-3 win over sixth-seeded Kaia Kanepi of Estonia. Kirilenko, a top-10 player last year, fell out of the top 100 this year after a knee injury kept her out of the first three months of the season. She needed a wild card to enter the Korea Open she won in 2008.
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.
Another American, Christina McHale, advanced when fourth-seeded Magadalena Rybarikova of Slovakia retired while trailing 6-2, 2-0. McHale will meet countrywoman Lepchenko for a place in the final. Lepchenko leads their head-to-head 3-1. Neither has won a WTA singles title.