Djokovic, 31, was the heavy favourite to win a sixth finals title but was outclassed 6-4 6-3 by the German.
Three straight aces brought up three set points, the second of which he took when Djokovic sent another forehand long.
The 21-year-old German has always been talked of as the leader of a pack of hungry young tyros aiming to unseat the multiple Grand Slam winners who have dominated the sport for well over a decade. Having said this, he'll need to be at his best on those key points today if he is to stand any chance of the title, as he faces Novak Djokovic, who looks back to his imperious best.
"It makes it so much easier for us to play so thank you for that".
The youngest end-of-season victor since Djokovic himself won this tournament a decade ago, Zverev is also the first German tennis player to win the ATP World Finals since Boris Becker claimed the accolade in 1995.
The victory extended Djokovic's record to 35-2 since the start of Wimbledon, a tournament he began ranked 21st after a right elbow injury interrupted his first half of the season.
"I didn't really play a very good match".
Yet this was a deserved victory for Zverev, who broke his opponent four times in total and finished the match with a vicious, curling passing shot which could very well have come from the boot of the watching David Beckham.
An increasingly-ragged Djokovic then dropped his opening two service games of the second set, either side of breaking Zverev for the first time as the German played a rare loose game.
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.
"I am incredibly happy obviously that this is my main title". I'd have preferred an option on +5 games in favour of Zverev, and in addition he's got a terrible career record at covering big handicap lines when a heavy underdog.
"He barely lost a match - but thankfully he did to me".
"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. But at the same time, as I said on the court, you put things in a larger perspective, see things a bit differently. Got back to world number one. "You are one of the best teams on tour so good luck for next year".
I think the time he had off earlier in the year rejuvenated him and made him realise how attractive tennis is and how much he still has to give.
Djokovic won Wimbledon and the US Open in 2018, as well as Masters 1000 events in Shanghai and Cincinnati.
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