MANILA, Philippines – Novak Djokovic ground down Roger Federer in his opening match at the ATP World Tour Finals to preserve his slim hopes of ending the year on top of the rankings. Djokovic, who beat Federer in last year’s final, must win at least two of his Group B matches to have any chance of toppling Rafael Nadal. World No. 7 Federer, who is bidding for a seventh title at the year-ender, produced some vintage play in the second set, but squandered his chances as the match went the distance. With the win, Djokovic extended his winning streak to 19, following his loss to Nadal in the U.S. Open final. -- Mornings @ ANC, November 6, 2013.