Australia's world No. 25 Samantha Stosur will face last year's Roland Garros runner-up Lucie Safarova in the final of the Prague Open clay-court event after both progressed from the semifinals Friday. Stosur went through after top seed Svetlana Kuznetsova withdrew before their scheduled semifinal clash Friday. The Russian world No. 13 pulled out complaining of a thigh injury, leaving Stosur to advance to a final on Saturday against Safarova, the 16th-ranked Czech who beat compatriot Karolina Pliskova 6-4, 7-6 (7-4). Serena's absence blows Madrid wide open In Madrid, in the absence of world No. 1 Serena Williams, who withdrew from the tournament Friday after suffering with flu, a whole host of players will be targeting victory at the WTA Madrid Open. Williams has played just three tournaments all season, losing in the final of the Australian Open and at Indian Wells. With the world's dominant player missing for so much of the season, 16 different women have already lifted WTA titles this year, with Sloane Stephens, Victoria Azarenka and Angelique Kerber the only multiple winners. That makes it hard to pick a winner for the tournament that starts this weekend, with Poland's Agnieszka Radwanska now the top seed, while five-time Grand Slam champion Maria Sharapova is still in the wilderness after failing a drugs test at Melbourne Park in January. Williams' conqueror at the Australian Open, Kerber, is in fine form after backing up her first Grand Slam by retaining her title on the indoor clay of Stuttgart last week. And the German is looking to build on her positive start to the European clay-court season in Madrid and Rome before the French Open next month. "I know I can play well on clay," said Kerber. "This is the attitude I'll take to Paris." The faster conditions than a normal clay surface in Madrid due to the slight altitude of the Spanish capital could help Kerber even more. Two-time champion Petra Kvitova returns to defend her crown at the Caja Magica and strongly believes the conditions favor her style. World No. 5 Azarenka is the most in-form player on the Tour as the Belarusian arrives in Madrid on the back of a 14-match winning streak having won in Indian Wells and Miami, as well as helping her country relegate Russia in the World Group II in the Fed Cup earlier this month.