Alexander Zverev became the first German for 23 years to lift the prestigious season-ending ATP Finals trophy with a stunning 6-4 6-3 victory over world No 1 and favourite Novak Djokovic.
Zverev produced a near-perfect performance to beat Djokovic and land the biggest title of his career in front of a capacity crowd at the O2 Arena in London.
Djokovic, who had gone unbeaten all week and hoped to equal Roger Federer's record of six ATP Finals titles, had won 35 of his 37 matches since July after making up for lost time following elbow surgery and poor form earlier in the season, winning Wimbledon, US Open, Cincinnati and Shanghai titles in a phenomenal five-month spell.
And after the pair shared their first two meetings - Zverev winning in the Rome Masters final last year while Djokovic defeated the German in emphatic fashion on his way to winning a record fourth Shanghai title last month - Djokovic then beat the 21-year-old 6-4 6-1 in the round robin stage here.
But having become the first German since Boris Becker in 1996 to reach the championship match with his stunning performance full of composure against Federer in the semi-final, Zverev then played the match of his life to beat a red-hot Djokovic.
Both players settled quickly, playing out a superb 29-shot rally in just the second point of the final, while Zverev was averaging 138 mph on his first serve - compared to 135 mph for the tournament - as he made his intentions clear.
Djokovic's irresistible serve was finally broken for the first time in five matches - comprising 40 consecutive service games - when Zverev struck in the ninth game before serving out the set in a real tale of the unexpected.
A topsy-turvy final took another twist at the start of the second set as the opening three service games were all shared, but Zverev, who has already captured three Masters 1000 crowns in his short career, held firm to move 3-1 up and he clinched a milestone win in the ninth game with a stunning backhand up the line.
He collapsed onto his back before Djokovic sportingly walked around to the other side to congratulate him.
Shot of the match
An unbelievable way to win your maiden ATP Finals trophy. Take a bow Sascha Zverev...
Zverev: My biggest title
"I am unbelievably happy. This is the biggest title I have won. I want to congratulate Novak on a great week and how you played in the second half of the season. You barely lost a match. We have never seen it before. I am actually very happy you lost one this week!"
Djokovic: Zverev deserves win
"You definitely played much better than in the group stage! You deserve it. You are still quite young but you have had an amazing career and I wish you all the best for your future. Speaking of being young I hope I will play many more years and I will see you guys here in the years to come."
What's next
The 2018 season comes to an end with the Davis Cup final next week in Lille when holders France host Croatia on the clay court at the Stade Pierre Mauroy. As for Djokovic and Zverev, it's rest and recuperation ahead of the start of the 2019 tennis season.