Novak Djokovic beats Tomas Berdych to progress to ATP semi-finals
Novak Djokovic beats Tomas Berdych at the ATP World Tour Finals at London's O2 Arena and puts victory down to his attitude.
The world number one defeated his Czech opponent 6-2 7-6 to go into the semi-finals as winner of Group A.
Djokovic joins Roger Federer in the knockout stages after he qualified from Group B on Thursday.
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