DUBAI — Defending champion Agnieszka Radwanska led a parade of top seeds into the Dubai Championships quarterfinals on a Wednesday overshadowed by the abrupt withdrawal of Serena Williams with a back injury. Williams, who became the oldest top-ranked woman on Monday, said she's had a sore back and ankle since the Australian Open, though she still reached the final in Doha, Qatar, last weekend. Her departure, announced 45 minutes before she was due to face 11th-ranked Marion Bartoli, came a day after second-ranked Victoria Azarenka, who beat Williams in the Doha final, withdrew with a right foot bone bruise. "I've just had some back problems the past couple weeks. It didn't get better," Williams said. "I thought it would get better as the week went on, but it didn't. I don't want to keep pushing it and make it worse." Former No. 1 Caroline Wozniacki joined Radwanska in the quarters, brushing aside an error-prone Zheng Jie of China 6-1, 6-0. Former US Open champion Sam Stosur got the better of Hseih Su-wei 6-4, 6-0. Former Wimbledon champion Petra Kvitova also got past former No. 1 Ana Ivanovic 7-5, 7-6 (1). The only upset on the day was fourth-seeded Angelique Kerber, who racked up 10 double faults in falling to Roberta Vinci of Italy 5-7, 6-1. In another match, Nadia Petrova of Russia defeated Carla Suarez Navarro of Spain 6-1, 6-0. Radwanska had a tougher-than-expected test in winning 7-5, 6-3 against Yulia Putintseva of Kazakhstan, who has only beaten two top 50 players. Slow to adjust to slower court conditions from the previous week in Doha, the fourth-ranked Radwanska was down a break in both sets. After a five-minute rain delay in the first set, the Pole broke back to make it 4-4 and then won the set when Putintseva missed easy shots. The 101st-ranked Putintseva broke to go up 2-1 in the second, but Radwanska broke right back and later won three straight games to finish off the match. On Tuesday, Stosur eased into the second round, brushing aside 19th-ranked Ekaterina Makarova 6-3, 6-1. — AP
