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.

It was past midnight in Turin when Djokovic completed a 7-6 (4) 6-7 (1) 6-3 victory after three hours and four minutes on court.

Rune has fared much better against Djokovic than most of his rivals over the last couple of years, beating him in Paris last autumn and Rome in the spring before a narrow defeat in the French capital a week-and-a-half ago.

The Serbian went on to claim the Masters series title, maintaining his record of not having lost a match since the Wimbledon final.

It was Rune who struck first with a break to lead 3-2 but Djokovic hit straight back and the high-class set went all the way to a tie-break, which the top seed took with a forehand smashed cross-court past his helpless opponent.

Rune reacted well, breaking again to lead 2-0 in the second set, but once more Djokovic found the immediate response, and a strong serve foiled the young Dane when he forced a set point at 4-5.

Rune slumped after reaching the Wimbledon quarter-finals prior to hiring Djokovic’s former coach Boris Becker last month, but there were plenty of moments here to demonstrate his huge talent and fearsome ball-striking.

He has won at least a set against Djokovic in every match they have played, but he had a helping hand in setting up a decider, his rival playing a highly unusual lacklustre tie-break.

Djokovic broke straight away to start the deciding set, only for this time Rune to recover the deficit immediately, prompting a frustrated Djokovic to stamp on two rackets, snapping the frames.

But he broke again to lead 4-2 and this time there was no way back for Rune.

Djokovic told Prime Video: “It took everything. I saw in the first game when he fired shots from the baseline, I knew it was going to be a tough night for me. I thought he played great. I played great in some moments.

“Overall a win is a win. It was a very emotional win and a tough win knowing the significance of tonight’s match. After a really terrible second-set tie-break I think I played a really solid third set.”

Earlier, Italian Jannik Sinner delighted the crowd by defeating Stefanos Tsitsipas in the opening singles match.

Sinner, 22, played as an alternate two years ago but qualified for the first time this season after claiming four ATP Tour titles and rising to world number four. He is one of the favourites to lift the trophy this week, which would be the dream scenario for the home fans, and a 6-4 6-4 victory over Tsitsipas is a big step towards the semi-finals.