Novak Djokovic begins title defence with victory against Marin Cilic

Novak Djokovic has begun the defence of his title at the ATP World Tour Finals with a comprehensive 6-1 6-1 victory over Marin Cilic.

The world number one, who has won this event for the past two years, lost the first set, but quickly hit back and broke his opponent in his second service game.

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From that moment it was one-way traffic and the Serb broke his opponent twice more to comfortably take the first set.

Despite a positive start to the second set, Cilic found himself 2-0 down after a number of errors, but he gave himself a chance by breaking Djokovic for the first time.

However, despite the backing of the crowd at the O2 Arena he was unable to level the scores as his opponent broke him once again, before winning the next three games to seal the match.