Tennis results: Novak Djokovic equals Roger Federer's record of six ATP Finals titles

The Serbian was pushed hard by 23-year-old Ruud but emerged after the 93-minute contest with a 7-5 6-3 triumph.

Ruud saved two break points in his first service game of the opening set to hold, but it set the tone for the match, with the Norwegian regularly forced onto the back foot.

There were a number of lengthy rallies during the match, including a 36-shot one in the final game to set up a championship point for Djokovic who then clinched the title with an ace.

In securing the crown for the first time since 2015, Djokovic equalled Roger Federer’s record for ATP Finals championships.

The former world number one was pleased with his performance and said the long wait for his sixth title made him appreciate the victory more.

“It’s finals, usually these kind of matches are decided by very small margins and one break of serve was enough in both sets,” Djokovic said.

“I knew Casper was playing really well coming into this match. I think we both served very well. I think in some decisive moments, like the 12th game of the first set, I just managed to put a few returns back in play, (to) make him run and make him play.

“I was really pleased with the way I was playing from the back of the court, particularly the forehand was looking to be really aggressive and it worked great, I am really pleased with the performance.”

He added: “A lot of nerves, particularly in that 30-all point, that was the longest rally of the match.

“As I said, you’ve got to stay focused the entire match, every single point. Momentum can shift to the other side very quickly.

“Seven years, it’s been a long time, but at the same time this – the fact that I waited seven years – makes this victory even sweeter and even bigger.”

Meanwhile, Joe Salisbury became the first British player to win the doubles title, alongside American partner Rajeev Ram.

The duo had lost the championship match last year, but were victorious this time around, beating Croatian pair Nikola Mektic and Mate Pavic 7-6 (4) 6-4 to lift the trophy.

“It’s very special,” Salisbury said. “I think it makes it extra special, being the first Brit. Hopefully there will be many more. There were three of us here this week. All did really well, had really good years. I’m sure there will be many more.

“But, yeah, really happy with it. I think it’s just special for us after coming so close in a couple of years. To get over the line this time feels amazing.”