Serbia's Novak Djokovic celebrates after winning against France's Jo-Wilfried Tsonga their Men's Singles Quaterfinals. – Photo by AFP

Serbia's Novak Djokovic falls as he plays with France's Jo-Wilfried Tsonga during their Men's Singles Quaterfinals tennis match. – Photo by AFP

Serbia's Novak Djokovic (R) shake hands with France's Jo-Wilfried Tsonga after winning their Men's Singles. – Photo by AFP

Roger Federer of Switzerland, right, hugs Juan Martin del Potro of Argentina, left, after he won his quarter final match at the French Open. – Photo by AP

Switzerland's Roger Federer serves to Argentina's Juan Martin Del Potro during their Men's Singles Quaterfinals match of the French Open. – Photo by AFP

Juan Martin Del Potro of Argentina returns the ball to Roger Federer of Switzerland during their quarter-final match. – Photo by Reuters

Angelique Kerber of Germany returns in her quarter final match against Sara Errani of Italy at the French. – Photo by AP

Sara Errani of Italy returns in her quarter final match against Angelique Kerber of Germany at the French. – Photo by AP