ATP World Tour Finals: Novak Djokovic caps his best season with title triumph

Photos: Fourth straight for Djokovic
Novak Djokovic of Serbia lifts the trophy after beating Switzerland's Roger Federer of Switzerland in the final of the ATP World Tour Finals.
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Photos: Fourth straight for Djokovic
Djokovic and runner up Federer of Switzerland pose with their trophies following the final at the O2 Arena.
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