Aiming to end a sensational year as he began it, Swiss master Roger Federer opened his bid for a seventh ATP Finals title with 6-4, 7-6(4) victory over American debutant Jack Sock on Sunday.
The 36-year-old was given a thorough workout by Sock although had he been a little more clinical the scoreline would have been more heavily-weighted in his favour.
Sock, who gate-crashed the end-of-season party when he burst from the pack to qualify by winning the Paris Masters, made the worst possible start when the second of two superb backhand winners gave Federer a break in the first game.
It was the only break of serve in the match, although Federer was always a step ahead of his 25-year-old opponent, who possesses one of the hardest forehands in the game.
Federer, the oldest player to qualify for the ATP Finals since 1970, looked aghast as two break points went begging at 3-3 and another two at 4-4 in the second set.
More stoic resistance by Sock saw him fend off more danger at 5-5 but Federer remained untouchable on serve and won 29 of 32 points on his delivery in the second set.
Federer jumped into a 4-2 lead in the tiebreak and although Sock finally took a point off the six-time champion's serve to level at 4-4, Federer reeled off the next three points to claim victory.
"It's always a struggle in the first match of any tournament," Federer, who took his grand slam title haul to 19 by winning the Australian Open and Wimbledon this year after missing the last six months of 2016 through injury, said.
"I got off to a great start, my big hope was I was going to be able to play a bit more freely after that.
"The second set was tight, I missed some opportunities, the breaker could have gone either way and in the end he helped me with some double faults and some mistakes."
Rafael Nadal, who was presented with the award for the year-end number one ranking, is scheduled to open his campaign for the only big prize to elude him on Monday against Belgium's David Goffin.