SYDNEY, Jan. 8 (Xinhua) -- Former Wimbledon champion Petra Kvitova defeated world No. 27 Lucie Safarova 7-6 (4), 6-2 to snatch her 300th career victory, reaching the last four of the Sydney International on Wednesday.
The second seed will face Bulgarian Tsvetana Pironkova, who is a semifinalist at Wimbledon in 2010, upsetting third seed Sara Errani of Italy 7-6 (2), 6-3.
American Bethanie Mattek-Sands, who upset top seed Agnieszka Radwanska, retired with a back injury while trailing fellow American Madison Keys 3-2 in their night quarterfinal.
Keys will face German fifth seed Angelique Kerber, who ousted Spaniard Carla Suarez Navarro 6-2, 6-4.
Kvitova thumped American Christina McHale 6-1, 6-0 in her opening match and is in a better frame of mind than last year, when she was a first-round loser to Slovakia's Dominika Cibulokva.
Kvitova, who beat Maria Sharapova for the Wimbledon crown three years ago, is the highest seed left in the Sydney draw following Tuesday's defeat of Agnieszka Radwanska.
Mattek-Sands said she withdrew to nurse her body through to next week's Australian Open and beyond.