Not even an elaborate volley played between the legs by Sock could get between Federer and an opening-round victory - although the sight of the American's backside in his face did knock the six-time champion off his stride very briefly. "But I didn't expect him to be this good yet".
"You can not forget that we played all the time on surfaces that he likes more than me", added Nadal.
Rafael Nadal and Roger Federer can set up a dream climax to the 2017 season at the ATP World Tour Finals, but organisers are sweating on the Spaniard's fitness and a new crop are itching to spoil the party.
Federer missed a year ago due to injury but the Swiss player has converted six of his 14 appearances to wins. "I'm working every day, practising well and just trying to be ready for the action".
Sock's nothing-to-lose approach produced an engaging contest but Federer's clinical play was too much for him.
In a freaky moment in the middle of the first set, the rookie American, playing in the showpiece event for the first time, hit a poor drop shot, inviting the simplest of put-aways.
There was a moment of levity towards the end of the first set when Sock, who had messed up an attempted drop shot, showed his posterior as a supposed target for Federer, who proceeded to hit the net. Taking on the power-hitters from the other Group, or Roger Federer is a whole other story though. "And like this, I can focus on playing the tournament, and not having to talk about that at the same time", Federer said.
Federer is chasing his seventh ATP Finals title after clinching his 50th win of the year against Sock on Sunday.
Sock started the second set in style, holding to love in a game sealed by a stunning cross-court forehand that left Federer stranded. "The crowd, the atmosphere is wonderful", Zverev, who reveled on the big stage, told reporters after the late-night finish. That's what I should have aimed for. He didn't quite get the better of his 25-year-old opponent's serve again until the second-set tiebreaker, but that was enough to win the match.