If the Serbian does claim the year-end number one ranking for a sixth time, he would match the record of Pete Sampras and victory at the end-of-season event would equal Roger Federer´s mark. That being said, this is still expected to be a tough match for Matteo Berrettini as he is playing against the number 2 seed.
"Sometimes, you know, the crowd is on your side, the majority of the crowd is on your side, and sometimes it's against you".
Berrettini, the last player to qualifier for the finals, walked towards the wrong exit after Djokovic's win was sealed on a first match point, and given the beating he had just taken, it was perhaps no surprise the Italian seemed slightly shocked.
Berrettini's forehand was responsible for 18 of those errors, including two shots into the net to hand Djokovic the only two breaks of the first set.
The Serbian, who has won 16 majors and is chasing the end-of-year number one ranking, said he had twisted "Roger, Roger" chants into Novak chants in his mind at Wimbledon.
After giving up that lone break to make it 4-1 in the second, Djokovic broke right back and then clinched the victory with an easy forehand putaway at the net. "Not allowed to lose anymore for me", Federer said.
"But, yeah, I've got to recover, I've got make sure I play better than today, and hopefully I can win that match".
The ATP Finals, featuring the year's best eight players, is contested in a round-robin format with the best four players and doubles teams reaching the knockout semi-finals stage. He also said he struggled a bit with the speed of the indoor hard court at the O2.
"But I really hope that I will be able to serve every single day a little better, and my goal is to be on Sunday serving normal".
Nadal, Daniil Medvedev, Stefanos Tsitsipas and Zverev are in Group Andre Agassi.
Roger Federer's pursuit of a seventh ATP Finals title got off to a poor start on Sunday when the Swiss great lost 7-5 7-5 to Austrian Dominic Thiem in his opening group match.
Nadal begins his campaign on Monday against defending champion Zverev.
Djokovic, who won the Australian Open and Wimbledon this season, must reach the final in London to have any chance of overtaking Nadal at the top of the rankings.