Maria Sharapova (L) of Russia and Li Na of China pose during the awarding ceremony of Porsche Tennis Grand Prix in Stuttgart, Germany, on April 26, 2013. Maria Sharapova won 2-0.(Xinhua/Ma Ning)

Maria Sharapova of Russia poses during the awarding ceremony after winning her final match of Porsche Tennis Grand Prix against Li Na of China in Stuttgart, Germany, on April 26, 2013. Maria Sharapova won 2-0.(Xinhua/Ma Ning)

Li Na of China reacts during the awarding ceremony after losing her final match of Porsche Tennis Grand Prix against Maria Sharapova of Russia in Stuttgart, Germany, on April 28, 2013. Li Na lose 0-2.(Xinhua/Ma Ning)

Maria Sharapova of Russia poses with the Porche awarded to her after winning her final match of Porsche Tennis Grand Prix against Li Na of China in Stuttgart, Germany, on April 26, 2013. Maria Sharapova won 2-0.(Xinhua/Ma Ning)

Li Na of China reacts after losing her final of Porsche Tennis Grand Prix against Maria Sharapova of Russia in Stuttgart, Germany, on April 28, 2013. Li Na lose 0-2.(Xinhua/Ma Ning)

Maria Sharapova of Russia celebrates after winning the final match of Porsche Tennis Grand Prix against Li Na of China in Stuttgart, Germany, on April 26, 2013. Maria Sharapova won 2-0.(Xinhua/Ma Ning)

Maria Sharapova of Russia celebrates during her final match of Porsche Tennis Grand Prix against Li Na of China in Stuttgart, Germany, on April 28, 2013. Sharapova won 2-0 to claim the title.(Xinhua/Ma Ning)

Li Na of China returns a shot during her final match of Porsche Tennis Grand Prix against Maria Sharapova of Russia in Stuttgart, Germany, on April 28, 2013. Sharapova won 2-0 to claim the title. (Xinhua/Ma Ning)

Maria Sharapova of Russia celebrates after winning the final match of Porsche Tennis Grand Prix against Li Na of China in Stuttgart, Germany, on April 26, 2013. Maria Sharapova won 2-0.(Xinhua/Ma Ning)

Li Na of China returns a shot during her final match of Porsche Tennis Grand Prix against Maria Sharapova of Russia in Stuttgart, Germany, on April 28, 2013. Sharapova won 2-0 to claim the title. (Xinhua/Ma Ning)

Maria Sharapova of Russia returns a shot during her final match of Porsche Tennis Grand Prix against Li Na of China in Stuttgart, Germany, on April 28, 2013. Sharapova won 2-0 to claim the title.(Xinhua/Ma Ning)

Li Na of China serves during her final match of Porsche Tennis Grand Prix against Maria Sharapova of Russia in Stuttgart, Germany, on April 28, 2013. Sharapova won 2-0 to claim the title.(Xinhua/Ma Ning)

Maria Sharapova of Russia celebrates after winning the final match of Porsche Tennis Grand Prix against Li Na of China in Stuttgart, Germany, on April 26, 2013. Maria Sharapova won 2-0.(Xinhua/Ma Ning)

Maria Sharapova of Russia celebrates after winning her final match of Porsche Tennis Grand Prix against Li Na of China in Stuttgart, Germany, on April 26, 2013. Maria Sharapova won 2-0.(Xinhua/Ma Ning)