Djokovic once again appeared to be under the weather, but he again summoned his inner strength to get the better of Ruud to win the season-ending title as he secured a 7-5, 6-4 victory in one hour and 32 minutes at the Pala Alpitour in Turin.
Two days ago, Djokovic struggled physically during his round-robin match against Daniil Medvedev as his right hand was shaking uncontrollably. However, he came through that match as he won in three sets to keep his unbeaten run at the Finals alive.
And he again appeared to have the shakes during the opening set against Ruud, but somehow shook it off to lift a fifth title in a disrupted 2022 season.
Besides equalling Roger Federer's record for most ATP Finals titles, Djokovic notched up a few other milestones along the way as he is now the oldest player to win the season-ending tournament at the age of 35, overtaking Federer's record (30).
Of course, he will also head home with the biggest cheque in tennis history as he will receive $4 740 300 and 1 500 ATP Ranking points as the undefeated champion.
Sunday's title was also his 91st, which leaves him just one behind Rafael Nadal in fourth place and 18 behind all-time leader Jimmy Connors' 109.
The opening set was a tight affair, but Djokovic always looked to be one step ahead of Ruud with the Norwegian saving two break points in game two and a third one in game eight.
But the 21-time Grand Slam winner was not to be denied in game 12 as a poor service game from the third seed opened the door and he barged his way in.
Djokovic went up a gear in the second set and this time the break came early as he edged ahead in game four and there was comeback from Ruud.
"Usually these kinds of matches are decided by small margins and one break of serve was enough in both sets," he said in a court-side interview.
"Casper was playing very well coming into this match, we both served very well. In some decisive moments in the match I managed to put a few returns back and make him play, make he run. I was looking to be aggressive and it worked."
Djokovic won his first five titles between 2008 and 2015 while he last played in a final in 2018. The seven-year wait has made it even sweeter.
He added: "A lot of nerves, particularly that 30-all point (late in the second set). You've got to stay focused during the entire match, momentum can shift to the other side very quickly. I missed a couple of forehands when I was serving for the match. I definitely felt nerves, but I am grateful to be able to serve the match out.
"Seven years, it's been a long time. At the same, the fact that I waited seven years makes this victory even sweeter."