![Juan Martin del Potro of Argentina returns a shot to Nikolay Davydenko of Russia during their Masters Cup tennis match in Shanghai November 13, 2008. REUTERS/Nir Elias (CHINA Stock Photo - Alamy Juan Martin del Potro of Argentina returns a shot to Nikolay Davydenko of Russia during their Masters Cup tennis match in Shanghai November 13, 2008. REUTERS/Nir Elias (CHINA Stock Photo - Alamy](https://c8.alamy.com/comp/2E7G978/juan-martin-del-potro-of-argentina-returns-a-shot-to-nikolay-davydenko-of-russia-during-their-masters-cup-tennis-match-in-shanghai-november-13-2008-reutersnir-elias-china-2E7G978.jpg)
Juan Martin del Potro of Argentina returns a shot to Nikolay Davydenko of Russia during their Masters Cup tennis match in Shanghai November 13, 2008. REUTERS/Nir Elias (CHINA Stock Photo - Alamy
![Roger Federer of Switzerland returns a shot to Radek Stepanek of Czech Republic during their Masters Cup tennis match in Shanghai November 12, 2008. REUTERS/Nir Elias (CHINA Stock Photo - Alamy Roger Federer of Switzerland returns a shot to Radek Stepanek of Czech Republic during their Masters Cup tennis match in Shanghai November 12, 2008. REUTERS/Nir Elias (CHINA Stock Photo - Alamy](https://c8.alamy.com/comp/2E77YYM/roger-federer-of-switzerland-returns-a-shot-to-radek-stepanek-of-czech-republic-during-their-masters-cup-tennis-match-in-shanghai-november-12-2008-reutersnir-elias-china-2E77YYM.jpg)
Roger Federer of Switzerland returns a shot to Radek Stepanek of Czech Republic during their Masters Cup tennis match in Shanghai November 12, 2008. REUTERS/Nir Elias (CHINA Stock Photo - Alamy
![Novak Djokovic Serbia Returns Ball Frenchman Editorial Stock Photo - Stock Image | Shutterstock Editorial Novak Djokovic Serbia Returns Ball Frenchman Editorial Stock Photo - Stock Image | Shutterstock Editorial](https://editorial01.shutterstock.com/wm-preview-1500/7585207g/17e32203/Shutterstock_7585207g.jpg)
Novak Djokovic Serbia Returns Ball Frenchman Editorial Stock Photo - Stock Image | Shutterstock Editorial
![Tennis Server ATP/WTA Pro Tennis Showcase - 2008 Tennis Masters Cup - Roddick Out, Radek In, Murray Through to Semifinal Tennis Server ATP/WTA Pro Tennis Showcase - 2008 Tennis Masters Cup - Roddick Out, Radek In, Murray Through to Semifinal](http://www2.tennisserver.com/images/photofeed/2008/masters-cup/singles.jpg)