Spanish second seed Nadal outclassed world number one Djokovic in a 6-0 6-2 7-5 win, which clinched a record-extending 13th title at Roland Garros.
Questions had been asked about 34-year-old Nadal's level, but he responded with an almost flawless performance.
Top seed Djokovic, 33, lost a completed match for the first time in 2020.
The Serb was overwhelmed by Nadal's rapid start and produced a despondent display as a result.
Defeat also meant Djokovic, who was bidding for an 18th Grand Slam title, lost ground on Nadal and Federer in their ongoing battle to finish with the most major wins.