India's Sania Mirza and her American partner Bethanie Mattek Sands have stormed into the Women's Doubles quarterfinals of the Dubai Tennis Championships. In their opening round match yesterday, the second seeded Indo-American duo defeated America's Liezel Huber and her partner from Chinese Taipei, Su-Wei Hsieh, in straight sets, 6-4, 6-4. For a place in the semi-finals, Sania and Bethanie will meet the Russian-Czech combination of Anastasia Pavlyuchenkova and Lucie Safarova today.Meanwhile, American Serena Williams, who on Monday became the oldest woman to top the women's world rankings, yesterday withdrew from the tournament, because of a lower back problem. This means that the tournament will be without the World Number one and number two, after Victoria Azarenka of Belarus pulled out on Tuesday due to a foot injury