Alexander Zverev (Ger) bt Marin Cilic (Cro) 6-4 3-6 6-4
Roger Federer (Swi) bt Jack Sock (US) 6-4 7-6 (7-4)
Tim Henman
Former British number one on BBC TV
The story of that first set was really the first game. Federer got a break-point opportunity and took it. For the rest of the 10 games it was pretty nip and tuck. When Sock gets a look at a second serve, he needs to be pretty disciplined.
Federer 6-4 Sock
And sealed with another ace.
Roger Federer takes the first set in 36 minutes. Routine for the Swiss after that break in the opening game.
Image source, Getty Images*Federer 5-4 Sock
Tunes belt out at the changeover as Federer sits in his chair contemplating how he'll try to serve out the set for what must be the billionth time in his career.
Silence falls and Federer quickly charges through the game, helped with another ace.
Two set points to Roger Federer.
*Federer 5-4 Sock
Chair umpire Mohamed Lahyani earns his money with a very loud and aggressive correction call as Jack Sock serves up an ace. That startled a few in the crowd.
And another ace from Sock. That's all he could do. Make Federer serve it out.
Federer 5-3 Sock*
In what feels like 30 seconds Roger Federer wraps up another service game.
After 31 minutes he's a game away from the first set.
*Federer 4-3 Sock
Oh. My. Word. He is human.
We can laugh because Roger Federer never does this but he has just missed a sitter.
At the net Jack Sock just pops the ball up into the service box. The American turns around, ready to take his punishment, expecting to lose the point but the Swiss maestro hits the tape!
The pair laugh about it on their way to the changeover. Jack Sock is just as shocked as the Federer fans in the crowd.
Jack Sock prepares to be hit by ball
Federer 4-2 Sock*
Nice. Jack Sock's best point of the match so far and it's the American's trademark. Big serve out wide, heavy top spin on the forehand and the put-away volley.
But he needs perfect points like that just to stay in touch here.
Sock goes for another big serve and it's another double fault. Deuce. Can Fed all-but seal the set?
Image source, ReutersDebate is under way at these Finals around the very future of the men’s game, with some serious rule changes being considered for the future following last week’s experimental NextGen Finals. Shorter sets, shot clocks, no advantage, no lets on serve, electronic line-calls...
Ross Hutchins, ATP chief player officer, on BBC radio 5 live: “The world is consuming sport in a rather different way and we want to engage the younger generation.
"All our research and advice suggests people like to consume sport in a shorter time. There is a new landscape out there that we need to keep in mind.”
Federer 4-2 Sock*
Roger Federer has shown very little emotion to far but his dad nods with approval in the crowd as he blasts another ace down the T.
Jack Sock has a first opening in a Federer service game though as he works his way to deuce.
That was a chance! Federer serves and volleys but can only pop the ball up at the net. Sock gets there but goes for the angle and finds the tramlines. Opportunity gone.
Image source, Getty Images
Russell Fuller
BBC tennis correspondent on 5 live
Federer is looking fairly comfortable - you can sometimes afford to lose a match in the round-robin system and still progress, but that won’t remotely be on Roger Federer’s mind.
*Federer 3-2 Sock
Good hold from Jack Sock and a big one at that. He needed that.
The American heads to his chair just the one break down.
Image source, ReutersFederer 3-1 Sock*
If he didn't know already from his three winless career matches against Roger Federer, Jack Sock seems to have decided he can't win this one in baseline rallies.
He plays the match's first drop shot successfully on the first point of the game on his way to 40-0 but then goes for two big second serves, both double faults, and suddenly the pressure is back on at 40-30.
Now the American sees another ball whistle past him off the Federer racquet. Deuce.
Federer 3-1 Sock*
Both men are in similar outfits today, Federer in a play purple/lilac shirt and Jack Sock in light grey.
That's about where the similarities stop in this game though, Federer serene at the back of the court and Sock scurrying around the baseline trying to stay in the rallies.
The American nicks a point but hardly moves as another ball flies past him to seal another game in Fed's favour.
Image source, Reuters*Federer 2-1 Sock
A nerve settler. Jack Sock has to work for it but gets his name on the board with a forehand winner at 40-30.
The crowd roar in appreciation for the American on his debut.
They may be backing Federer to win this one but they want their money's worth.
Federer 2-0 Sock*
That was by no means the start American Jack Sock was after. He must be have been a little stunned after that.
Federer starts his first service game with an ace to compound the American's issues but the crowd are shocked into silence as the great man makes an error and a double fault and suddenly we're at deuce.
No bother though. Federer stays solid to see his way through and put his second game on the board.
Image source, Reuters
Andrew Castle
BBC Sport tennis commentator
I can’t believe what I’m watching with Roger Federer sometimes, I really can’t. That game was virtually perfect.
Sock 0-1 Federer*
"Welcome to my court, Jack".
What a start from Roger Federer.
Two backhand winners and the Swiss breaks serve to take the opening game in a flash. That will send a shiver down the spine of Jack Sock on his first appearance here.
Image source, ReutersFederer 0-0 Sock*
Right then here we go.
Jack Sock to serve first.
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Federer v Sock
Image source, Getty ImagesBut Roger Federer's bid for a seventh Tour titles may not be straight forward.
His opponent today Jack Sock is the man in form. The 25-year-old won the Paris Masters last week to sneak into this event as the last man to qualify.
That victory saw him jump up to a career high ninth in the world rankings.
He is yet to go past round four of a Grand Slam but will bring a big serve and aggressive game to his first Tour finals.
Federer v Sock
Image source, Getty ImagesRoger Federer came into 2017 having missed half of last season, without a Grand Slam title to his name since 2012.
He ends it with Major number 18 and 19 in the bag after remarkable victories at the Australian Open in January and Wimbledon in July.
The Swiss 36-year-old arrives in London as the strong favourite despite an early exit at the US Open in September and injury issues at the end of this campaign.
He won the Swiss Indoors title last month, his seventh title of the year, and says he is "fine" ahead of his quest for a seventh ATP Tour Finals crown.