Nikolay Davydenko wins ATP World Tour Finals 2007 in London . Russian beats Argentine Martin Del Potro of Argentina in straight sets . Serbian was beaten in last year 's final by Serbian Novak Djokovic . Bryan brothers win doubles title to claim end of season top ranking .
Nikolay Davydenko wins ATP World Tour Finals title in London . Russian beats Juan Martin Del Potro of Argentina in straight sets . Davydenko was beaten in last year 's final by Serbian Novak Djokovic . Bryan brothers win doubles title to claim end of season top ranking .