The Federer-loving crowd were in uproar and to make matters worse Zverev composed himself and slammed down a 137mph ace to level the breaker at 4-4.
The German man converted both of his break point chances, with Federer going one from three, and ultimately the match revolved around these five points, as well as the second-set tiebreak.
Zverev made a vital hold from 0-30 down at 3-2, picking up a handsome volley near his feet as Djokovic fought desperately to regain parity.
Zverev even began to win the longer rallies, an area of the game that Djokovic usually dominates. "I'm incredibly happy and incredibly proud of this moment right now", he added. "It's the biggest title I've won in my career", said Zverev, who already has three Masters titles to his name. We see each other a lot. "I'm very sorry that this happened I didn't mean to upset anybody - that's all I can say, sorry".
"The crowd have been absolutely fantastic all week". You are still quite young but you have had an wonderful career so far and I wish you all the best for your future.
He looks a potential successor to Steffi Graf and Boris Becker as a great German tennis player, probably with more potential than Wimbledon champion Angelique Kerber, and is the first from his country to have won this regular season-end event since Becker in 1995. Federer won just one point after that as Zverev wrapped up the match.
The world number one eased past Kevin Anderson in yesterday's evening match, for the loss of just four games, winning a whopping 63% of points in the match in a dominant display, and is priced at just [1.17] to be lifting the trophy tonight.
"Obviously us young guys, we're coming through", he said.
Obviously, it is quite astonishing, winning this title, beating two such players back-to-back, Roger [Federer] and Novak, in semi-finals and final.
Although he came up against an inspired opponent in Zverev, Djokovic faltered particularly on his forehand and never managed to dictate play in the final.
"Sascha (Zverev) definitely played much better than he did in the group stage", he said. "He deserved to win, he's still quite young but he's had an fantastic career so far and I wish him all the best for his future", said Djokovic. "But at the same time, as I said on the court, you put things in a larger perspective, see things a bit differently", he said.
"I want to apologize for the situation in the tiebreak", said Zverev, who was booed by some of the crowd during his on-court interview.
Thank you for supporting tennis for 11 months in a year.
"Last but not least, you fans have made this tournament very special for all of us".
To come back after a hard start to the year and an injury to win Wimbledon and the US Open this year, and become the dominant player in the second half of the year, speaks volumes for his mentality and love for the game.