Djokovic into semi-finals of World Tour Finals 2013

The current champion Novak Djokovic beat Juan Martin Del Potro in a tough three sets 6-3 3-6 6-3 to book his place in the semi-finals of the World Tour Finals. Djokovic extends his winning streak to 19 consecutive victories since losing to Nadal at the US Open in September. On Saturday Federer and Del Potro will play for the second Group B qualification place.