Russia’s Karen Khachanov defeated incoming world number one Novak Djokovic to win his first Masters 1000 title at the Paris Masters.
The 22-year-old beat Djokovic 7-5 6-4 in one hour and 37 minutes to end the Serb’s 22-match unbeaten run.
Fourteen-time Grand Slam champion Djokovic, 31, will still overtake Rafael Nadal at the top of the world rankings on Monday.
“It means the world to me,” said world number 18 Khachanov.
“It’s one of the biggest titles in my career so far. I couldn’t be happier to end the season like this, to win against Novak Djokovic, the number one in the world.”
Khachanov will rise to world number 11 on Monday and becomes the first Russian since Nikolay Davydenko in 2009 to win a Masters 1000 title.
He hit 31 winners as he pulled off one of the shocks of the tennis year in his final tournament of the season.
Djokovic, who has been suffering from flu-like symptoms all week, added: “I don’t feel too good today but I’d like to give respect to Karen for playing a great match today and he deserves to win.
“He deserves his trophy and I am sure we will see a lot of great matches from him in the future.”
Victory would have marked Djokovic’s fifth Paris Masters title but he was not allowed to settle into Sunday’s match and was undone when Khachanov broke his serve at 5-5 before going on to win the first set.
Khachanov broke early in the second set and threw away three further break points in the seventh game, but was able to capitalise on his advantage and hold on for the win.
BBC tennis correspondent Russell Fuller
Marat Safin – to whom Karen Khachanov has often been compared – won the Paris Masters three times, but lost his first final to Andre Agassi.
He went on to win the Australian Open and the US Open, and Khachanov seems to have the key ingredients required to follow in his footsteps.
The Russian showed power, composure and patience to win the title, and as a result will move up to number 11 in the rankings.
Djokovic may not have been in peak physical condition after contesting that three hour semi-final with Roger Federer, but what a scalp for Khachanov to take in his first Masters final.
Before today, the Serb had lost only one of the 32 matches he had played since the start of Wimbledon.