Defending champion and top seed Nadia Petrova retired ill against Melinda Czink of Hungary in the Bell Challenge quarterfinals on Friday.

Petrova and Czink went serve for serve until they went into a tiebreaker, which fifth-seeded Czink won 7-4, after which the Russian quit playing.

Czink will line up on Saturday against third-seeded Aleksandra Wozniak, who kept Canadian hopes alive of a home champion by dispatching Alla Kudryavtseva of Russia 6-1, 6-1 in 53 minutes, conceding only six points on serve. Wozniak, back in the semis for the second year in a row, lost to Czink at Birmingham in June.

Fourth-seeded Lucie Safarova of the Czech Republic reached her first semifinals of the year when she beat 2008 finalist Bethanie Mattek-Sands of the United States 6-3, 6-4 at the Bell Challenge on Friday.

Safarova recovered from 4-2 down in the second set to win her first quarterfinal this year in six chances.

Next, she will play eighth-seeded Julia Georges of Germany, who matched her career-best performance of making the last four after beating qualifier Lilia Osterloh of the United States 6-2, 6-4.