BBC Sport - ATP World Tour Finals: Novak Djokovic relishes No 1 ranking

Number one ranking delights Djokovic

Novak Djokovic says it is "an incredible achievement" to end the year as world number one after beating Tomas Berdych at the ATP World Tour Finals.

The Serb, who won 6-2 6-2 to extend his unbeaten run indoors to 30 matches, will face Japan's Kei Nishikori in the semi-finals on Saturday.

Watch live coverage of Djokovic v Nishikori on Saturday on BBC Two, the BBC Sport website and on Connected TV from 14:00 GMT, with commentary of both semi-finals on Sports Extra.