Roger Federer had never lost his opening match at the ATP World Tour Finals since the elite tournament moved to London in 2009. On the back of a chaotic and disappointing season, the former World No. 1 was beaten on Tuesday for the second time in less than a week by defending champion Novak Djokovic 6-4, 6-7 (2), 6-2. The Serb extended his winning streak to 18 matches after capturing his sixth title of the season last week in Paris, where he defeated Federer in the semifinal. Djokovic kept alive his chances of overtaking Rafael Nadal in the race for the year-end No. 1 spot. More...