Djokovic had not been beaten since Stefanos Tsitsipas knocked him out of the Rogers Cup in August, but the new world number one came unstuck against another rising star on Monday (AEDT).

The unseeded Khachanov struck 31 winners in an imperious performance, denying the 14-time grand slam champion a record-equalling 33rd Masters title with a 7-5 6-4 upset in Bercy.

Djokovic beat Roger Federer in a classic semi-final on Saturday, but failed to match the standards he set on a remarkable winning run as Khachanov rose to the occasion in his first Masters final.

The Russian won 76 per cent of points behind his powerful first serve and broke three times, coming from 3-1 down in the first set before going on to win his third title of the season - and a fourth of his career.

Djokovic will replace Rafael Nadal at the top of the rankings on Monday, but was unable to match the Spaniard's tally of Masters triumphs ahead of the season-ending ATP Finals in London. 

A fired-up Djokovic let out a roar and pumped his fist after taking a 3-1 lead when Khachanov drilled a backhand wide under pressure, but the underdog was undeterred and broke back immediately.

Khachanov was enjoying himself, prowling around the court with vigour and going a break up at 6-5 after keeping Djokovic at bay with resolute defence before the Serbian netted when a backhand was fired at his feet.

A rasping serve down the tee sealed the set for the 22-year-old, with Djokovic looking flat and in need of inspiration.

The composed Khachanov maintained his momentum, breaking to lead 2-1 when Djokovic put a backhand into the net and showing lightning sharp reactions to put away a volley at the net as he continued to put the favourite under pressure.

Djokovic saved three break points to reduce the deficit to 4-3, but Khachanov did not allow him a sniff of a break back and sunk to his knees to plant a kiss on the court after an errant backhand from the four-time Paris Masters champion secured the upset.