Djokovic, who lost to the Greek player in the Shanghai quarterfinals three weeks ago, did not concede a break point to Tsitsipas.
It could have been an even quicker victory, considering Tsitsipas saved three set points at 0-5, 0-40 in the first set and held serve.
Djokovic, a four-time champion in this event, broke Tsitsipas in the third game of the second set, then held and broke to love for 4-1. Tsitsipas, who dropped his serve four times, appeared to hurt his left ankle when retrieving a shot near the baseline in the second set.
Djokovic, last year’s runner-up, is bidding for the year-end No. 1 ranking. He next plays US Open semifinalist Grigor Dimitrov, who reached his second semifinal this season by beating Cristian Garin 6-2, 7-5.
Nadal is guaranteed to finish the year as No. 1 if he wins the Paris Masters for the first time.