Novak Djokovic has eventually tamed Danish debutant Holger Rune with a 7-6 (7-4) 6-7 (1-7) 6-3 victory in his opening round robin match at the ATP Finals to seal the year-end No.1 ranking for a record-extending eighth time.
The 36-year-old Serb was stretched to the limit at times on Sunday with Rune producing some fireworks for the large evening crowd in Turin's cavernous Pala Alpitour.
But after an uncharacteristically poor second-set tiebreak, Djokovic made his experience count as he began his quest for a record seventh title at the year-ender.
"It took everything. The first game he was firing shots and I knew it would be a tough night," Djokovic, who now boasts an 18-1 record in his opening match at the tournament, said.
"He played great and I played great in moments. It was an emotional win knowing that I would clinch the world No.1."
— ATP Tour (@atptour) November 12, 2023
Earlier on day one, Jannik Sinner made a dream start in front of his home crowd with a 6-4 6-4 defeat of Stefanos Tsitsipas in their opening Green Group clash.
Djokovic will next face Sinner on Tuesday knowing his 19th successive win ended any chance of Spain's Carlos Alcaraz overtaking him in the rankings this week.
After this tournament, Djokovic will become the first player to hold No.1 for 400 weeks, with Roger Federer at 310 the only other man to eclipse the 300-week mark.
If the Serb raises the trophy next weekend, he'll break a tie with Swiss legend and capture a record seventh title at the finals.
Djokovic has won 19 straight matches stretching back to his five-set loss to Alcaraz in July's Wimbledon final.
Playing in front of his home crowd, world No.4 Sinner was streets ahead of Tsitsipas even if the score looked reasonably close.
Sinner served superbly throughout and struck his groundstrokes with venom, needing just one service break in each set to wrap up a routine victory.
The 22-year-old claimed the opening set in 40 minutes and when he broke serve at the start of the second set he never looked like relinquishing control against a flat-looking Tsitsipas.
The Italian, who has qualified by right for the season-ender for the first time, sealed victory with an ace.
"It was a long week before coming here and I was excited to finally step on court," the 22-year-old Sinner said.
"I knew it would be tough but I think I answered the questions really well.
"It's a special week, such an incredible feeling playing here with the roof closed and the crowd."