Novak Djokovic ensured he will finish the year ranked world number one for an eighth time after battling to a late-night victory over Holger Rune in his opening match at the ATP Finals.
Djokovic is chasing a record seventh title but again found 20-year-old Rune, who is making his debut at the eight-man event, a troublesome opponent before pulling off a third win in five meetings.
