Nadal is 1,460 points clear of Swiss world number two Roger Federer in the world rankings and victory over Chung ensured him an unassailable lead before the World Tour Finals in London later this month.
"I'm very, very happy for everything", Nadal told Sky Sports.
Federer is skipping Paris after winning back-to-back titles in Shanghai and Basel and is resting to be prepared for the ATP Finals starting in less than a fortnight in London. He also finished 2008, 2010 and 2013 atop the rankings.
This result sees Nadal progress to the last 16, but more importantly for the Spaniard, finish the year as the number one for the fourth time. It's been an awesome year, ' he said after the match.
"One year ago, for sure, I never dreamt about being No. 1 again at the end of the season so it's something that means a lot to me".
However, it wasn't plain sailing for Nadal against the 21-year-old Chung, who is due to feature at the inaugural NextGen ATP Finals in Milan next week.
But Nadal's South Korean opponent, who is ranked world No.55, didn't make the game easy for Nadal and pushed him in the early games. But Nadal accelerated away after that and served out the victory on his second match point when Chung hit a forehand long.More news: Trump calls NYC truck attack suspect 'animal', vows immigration crackdown
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Nadal has enjoyed fantastic success in Paris, winning the French Open 10 times at Roland Garros, but he has never won the title at Bercy. He will next face Pablo Cuevas of Uruguay.
Earlier on Wednesday, fourth seed Alexander Zverev was dumped out by Haase in a 3-6, 6-2, 6-2 second-round defeat.
Home hope Lucas Pouille kept his slim hopes of qualifying for the World Tour Finals alive by seeing off Spaniard Feliciano Lopez 6-3, 6-4, but US Open runner-up Kevin Anderson's chances ended with a 5-7, 6-4, 7-5 loss to Fernando Verdasco.
Haase next plays No. 13 Juan Martin del Potro, who eased past Joao Sousa of Portugal 6-2, 6-2.
Rolex Paris Masters against Chung as if he had won a grand slam tournament, but not far.
But the 31-year-old Spaniard - who is also trying to balance the delicate political situation in his native country with his status as an worldwide sportsman - refused to hype up his potential coronation.