Kvitova, Kerber advance in Sydney; Errani out

Sydney, Australia ( - Petra Kvitova and Angelique Kerber were among the quarterfinal winners Wednesday at the Sydney International, but Sara Errani was bounced by Tsvetana Pironkova.

The second-seeded Kvitova battled through a tough first set before cruising in the second for a 7-6 (7-4), 6-2 win over fellow Czech native Lucie Safarova, while the fifth-seeded Kerber rolled to a 6-2, 6-4 triumph over Spain's Carla Suarez Navarro.

Kvitova, playing her first event of 2014, will next face Pironkova, who pulled off a 7-6 (7-2), 6-3 win over the third-seeded Errani on Wednesday.

Kerber, a quarterfinalist last week in Brisbane, will battle American Madison Keys in Thursday's semifinals. Keys moved on when fellow American Bethanie Mattek-Sands retired with a back injury after just five games. Mattek-Sands had knocked off top seed and defending champion Agnieszka Radwanska in the second round.

This is the final tune-up for the Australian Open. The first Grand Slam event of 2014 is set to get underway Monday in Melbourne.