It was a solid display from the six-time ATP Finals champion, who sailed through his service games, never facing a break point, and he broke Jack once in the first set to notch a quick triumph that will boost his chances of reaching the semi-final for the 14th time in 15 appearances.
"In the second, he caught a serving rhythm".
"If you asked me "do you want changes?' I will say 'no", he said.
"I can't predict what might happen in the next couple of days, but my feeling is that I'm here to play and to try my best".
Eight-time Grand slam victor and American legend Andre Agassi believes that Roger Federer is the favourite to win the ATP World Tour Finals as Rafael Nadal does not do well late in the year because of "wear and tear".
But Nadal, victor of the French and US Opens, was guaranteed finishing the year as number one for the first time since 2013 after Federer withdrew from the Paris Masters to rest his body.
Should he be fit, Nadal will relish the opportunity to play against Federer to erase the memories of losing to him five times in a row. He just couldn't convert them. Federer won the final two points on his serve to go to 1-0 in the round robin. Federer got to it and hit a backhand victor. "It landed just inside both lines", said Sock, who still won the game. I know it can be somewhat intriguing but at the same time the longer sets allow you to stretch a lead, it's more comfortable at times. It's Roger, I guess.
Another light-hearted moment came when Sock hit a shot that should have set up an easy victor for Federer.
But as he ran up to return the ball, Sock turned around and bent forward at the net, showing his backside to Federer. "That's what I should have aimed for", he joked.
Federer is chasing his seventh ATP Finals title after clinching his 50th win of the year against Sock on Sunday. His last one came in 2011.
Sock is one of four players to qualify for the tournament for the first time.
After the Federer match, Rafael Nadal was given his trophy for finishing the year as the No. 1 player in the rankings.
Earlier, the ATP had announced a series of rule changes and innovations for experimentation at the Next Gen ATP Finals in Milan.