Novak Djokovic will finish the year as world number one for a record-extending eighth time after beating Holger Rune 7-6 (7/4), 6-7 (1/7), 6-3 in his opening match at the ATP Finals on Sunday.

The 24-time Grand Slam champion needed just one win or a defeat for young rival Carlos Alcaraz in order to secure top spot in the ATP rankings for 2023 and prevailed in a three-hour Green Group clash with spirited debutant Rune.

Djokovic, on a run of 19 straight wins, has had an age-defying year, winning three Slams to become the all-time record winner of major titles.

The 36-year-old came into the Finals in Turin off the back of his seventh triumph at the Paris Masters, his 40th victory at a Masters 100 event.

Those are two more records to add to a long and growing list for Djokovic, who is hunting a seventh Finals title which would take him one ahead of retired great Roger Federer.

"It means a lot. You could see that there were a lot of emotions on the court," said Djokovic.

"I could feel it, I was very eager to win the match and get that monkey off my back... Obviously a big objective, a big goal has been achieved, everything else now is a bonus."

Djokovic looked on course for victory when he took a brutal opening set in decisive fashion, prevailing in the tie-break with a stunning cross-court return winner.

And the match looked to have turned decisively in the third game of the second set, when after Rune won the first two Djokovic broke back in a brilliant 11-point game eventually won at the third attempt.

Rune kept plugging away, however, and after the pair slugged each other with bigger and bigger hits Djokovic slipped in the tie-break, missing a simple volley to draw level on the second point and then collapsing to concede the set.

But after briefly losing it for allowing Rune to break back in game three of the third set, kicking his rackets in a rage, Djokovic composed himself and saw out a historic win.

"I found a way to win today against an opponent who played brilliantly... he had a lot of courage today," added Djokovic in Italian.

"If I want to keep up with these youngsters I'm going to have to work even harder!"

Sinner off the mark 

Home hope Jannik Sinner got off to a near-perfect start by beating Stefanos Tsitsipas in straight sets, 6-4, 6-4, delighting the crowd in Italy's northwest.

Sinner has had the best season of his career to date, winning four tournaments and is set to become the first Italian ever to finish a season in the ATP top five.

The 22-year-old comfortably dealt with 2019 champion Tsitsipas in front of an enthusiastic crowd, not dropping a service game nor facing a break point in the whole match.

"The atmosphere was really, really nice. It's huge pleasure for me to play here in Turin, in Italy," Sinner told reporters.

"Obviously a little bit more pressure, but I managed it really well today, so I'm happy."

Afterwards Greek Tsitsipas denied he had any physical problems even though he looked way below his best, telling reporters "I'm healthy. I'm ready to compete."

The 25-year-old had to play down reports of an elbow injury which curtailed practice ahead of his tournament opener.

"I'm absolutely fine and I'm ready to play this tournament. Turin is one of the most important events of the year for me," he said.

On Monday Alcaraz makes his ATP Finals debut in the Red Group against Alexander Zverev, the second seed Djokovic's closest challenger.

However the Wimbledon champion is in uncertain form after being dumped out of the Paris Masters by Russian qualifier Roman Safiullin following return from an injury lay-off.

The Spaniard hadn't played since the Shanghai Masters in early October due to lower back and left foot problems.