With defending champion Andy Murray, Novak Djokovic and Stan Wawrinka all absent from the Tour Finals due to injury, Federer and Rafael Nadal are the unquestioned headline acts.
It was a fairly accurate description of Federer's astonishing year in which, after a six-month lay-off at the end of 2016, he returned to win the Australian Open and Wimbledon to reach 19 grand slam titles.
Federer didn't have it so easy as Sock found some rhythm in the second set, but the Swiss held his nerve to take it in a tie-break.
Federer broke Sock, who was making his debut at the tournament, in the very first game, hitting a backhand victor to take the 1-0 lead.
Sock is the first American to win a Masters title victor since Andy Roddick at the 2010 Miami Open and he'll finish the year at the number one US player for the first time in his career ahead of Sam Querrey and John Isner.
Sock was on the way to level the match after losing the first set 7-5, leading 5-1 in the second Mohamed Lahyani called a halt to proceedings. He just couldn't convert them.
At 3-2, he was 40-15 up on serve but Zverev, wound-up by an erroneous over-rule, forged back to break with an exquisite lob.
Cilic then dropped serve to love at 4-5 to lose for the sixth time in seven matches at the year-ender.
Fans hoping for some young blood to challenge Federer and Nadal will get a glimpse of a potential future star when Germany's Alexander Zverev makes his tournament debut against Croatia's Marin Cilic later on Sunday. I figured it was going to go out. "It landed just inside both lines", said Sock, who still won the game. "But, I don't know". 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.
Augusta would've been nice but Sock is no doubt relishing the chance to compete against the tennis elite - including the likes of Roger Federer and Rafa Nadal - at one of the biggest events of the year outside of the majors at London's O2.
"It was a big distraction, I'll tell you that", Federer joked about Sock's backside, "because it was very big. That's what I should have aimed for".
He came into 2017 having missed half of last season due to fitness problems and was without a Grand Slam title since 2012.
Sock is one of four first-time qualifiers here, having crept through the back door by winning the Paris Masters. Zverev, Grigor Dimitrov and David Goffin also qualified, though Goffin played in the tournament previous year as an alternate after Gael Monfils withdrew.
Zverev, bidding to become the first German to finish the year in the world's top three since Boris Becker in 1994, will face a mouthwatering clash with Federer on Tuesday.
Nadal, twice a Tour Finals runner-up, is due to open his campaign against David Goffin on Monday, however the Spaniard admits he is still struggling with the knee problem that forced him to pull out of the recent Paris Masters.