Kvitova to play Pironkova in Sydney semifinals
In other women's play, defending champion Elena Vesnina retired from her second-round match at the Hobart International with a back injury. Spanish qualifier Estrella Cabeza Candela was leading the match 4-6, 6-2, 4-1 when Vesnina quit.
At the ATP tournament in Auckland, New Zealand, American wild card Jack Sock defeated second-seeded German Tommy Haas 6-4, 6-4. American John Isner, the third seed, also advanced with a 7-6 (1), 3-6, 6-2 win over Slovakian Lukas Lacko.