India's Sania Mirza and her American partner Bethanie Mattek Sands will today slug it out for a Women's Doubles semi-final berth in the WTA Dubai Tennis Championships. The second seeded Indo-American duo will meet the Russian-Czech combination of Anastasia Pavlyuchenkova and Lucie Safarova.In their opening round match yesterday, Sania and Bethanie had defeated America's Liezel Huber and her partner from Chinese Taipei, Su-Wei Hsieh, in straight sets, 6-4, 6-4.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 World Number two, after Victoria Azarenka of Belarus pulled out on Tuesday due to a foot injury.In the Women's Singles quarterfinals today, third seed Agnieszka Radwanska of Poland will lock horns with Petra Kvitova of the Czech Republic, Caroline Wozniacki of Denmark will play against Marion Bartoli of France, Italian Roberta Vinci will clash with Aussie Samantha Stosur and Russia's Nadia Petrova will take on Sara Errani of Italy.