Roger Federer's withdrawal from the Paris tournament in order to rest ahead of the ATP Finals meant Nadal needed only one win to guarantee his great rival could not catch him and he avoided any slip-ups against 54th-ranked Chung, although the 21-year-old did cause Nadal problems.
Nadal, who is tied for a record 30 Masters titles with Djokovic, has never won the tournament in Paris.
Nadal was also crowned year-end No.1 in 2008, 2010, 2013, his title this year is incredibly impressive considering he was seeded No.9 at the Australian Open earlier this year.
Rafael Nadal will finish the year as the top-ranked male tennis player for the fourth time.
"But yes, here we are, (it) happened". Means a lot, no?
"I'm very very happy for everything. After nearly 10 years since the first time".
Nadal will next face Pablo Cuevas in the last 16 on Thursday, after the unseeded Uruguayan edged out Albert Ramos-Vinolas 6-7 (5/7), 7-6 (7/1), 6-2.
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Federer has beaten Nadal four consecutive times - not dropping a set in three of them - and the 19-time grand slam champion was in outside contention for the No.1 ranking before pulling out of Paris to focus on the season-ending ATP Finals in London next week.
The 16-time Grand Slam champion did not have it all his own way in a see-sawing first set in which he and Chung exchanged two breaks apiece before Nadal broke to love in the final game.
The 20-year-old German lost his composure after easing through the first set, as his bid for a third Masters title of the season was abruptly ended.
In remaining first-round play, Britain's Kyle Edmund rallied from a set and 3-0 down and saved match point before beating Evgeny Donskoy of Russian Federation 5-7, 7-6 (7), 6-3.
Fourth seed Alexander Zverev looked jaded in a surprise 3-6, 6-2, 6-2 loss to Dutchman Robin Haase in his opening match.
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.