The 19-year-old rallied from a set down to overcome Djokovic 3-6 6-3 7-5 and deny the Serb a seventh title in the tournament, capping off a spectacular run in which he also beat four other top-10 players.
"To beat Novak. To be able to beat him in such occasion ... in the final is probably the best feeling of this whole week," said Rune, who defeated Hubert Hurkacz, Andrey Rublev, Carlos Alcaraz and Felix Auger-Aliassime en route to the title clash.
"It was also important for me to beat Felix and Alcaraz and these guys. But still, to be able to beat Novak ... he's probably one of the greatest we have ever had in this sport.
"It's a crazy feeling."
Rune, who climbed to world number 10, withdrew from the Next Gen ATP Finals and will now head to Turin as the first alternate at the season-ending ATP Finals, which begins on Sunday.
"Of course I'm going to go to Turin. I'm one out. I mean, I wish all the players that I'm not going to play, because I wish them to be healthy, but at the same time it would be awesome if I got to play," Rune said.
"I didn't expect that at all four or five weeks ago but now I'm here. I'm super happy how I officially ended my season, and if there possibly is more matches, I'm super excited for it."
