Katerina Siniakova of the Czech Republic posted a 7-6 (2), 6-2 upset of No. 4 seed Daria Kasatkina of Australia in the second round of the Korea Open on Thursday in Seoul.

Kasatkina rallied from down 5-2 in the first set to force a tiebreaker. In the second set, she was broken three times and lost the final four games. She had eight double faults and won only half the points (22 of 44) on her first serve. Siniakova saved six of nine break points.

The top two seeds, who also played their first matches on Thursday, advanced to the quarterfinals. Top-seeded Iga Swiatek of Poland breezed past Romania’s Sorana Cirstea 6-3, 6-2. No. 2 Ekaterina Alexandrova of Russia rallied to beat Lois Boisson of France 4-6, 6-2, 6-2.

There were a few more upsets of lower seeds in competition. Dutch competitor Suzan Lamens knocked off No. 5 Diana Shnaider of Russia 6-4, 6-2 and will face Siniakova in the quarterfinals.

German qualifier Ella Seidel upset sixth-seeded Beatriz Haddad Maia of Brazil 6-7 (4), 7-6 (3), 7-5 in a back-and-forth battle which lasted 3:28. She will meet Alexandrova for a spot in the semifinals.

–Field Level Media