Djokovic unbeatable? Federer eyes two wins in a week

Beating Novak Djokovic has been beyond virtually every player this year but Roger Federer has the chance to get the better of the Serb for the second time in a week on Sunday. The 34-year-old ended Djokovic's 23-match winning streak on Tuesday with a classy straight-sets victory in the group stage of the ATP World Tour Finals but knows he will need to be at least as good to repeat that feat in the final.