Jack Sock berates himself as he bangs another forehand into the net. Now wide with the same shot two points later.

Federer is piling the pressure on. 30-30.

Big point. In comes Federer. Volley winner.

Break point again for the Swiss.

No hint of nerves from Roger Federer. The first serve keeps finding the serves box despite the scoreline.

After a 10 minutes service game last time for Sock, Federer wins his in 78 seconds.

No let up.

Now Jack Sock does battle through as Federer can only punt the return of a big serve into the net.

But how much did that take out of the American in this closing event of the season? He changes his shirt at the changeover.

Federer will serve to stay in the set. Can Sock apply the pressure?

Image source, Reuters

Eight minutes gone in this game now and Jack Sock still can't find a way out of it.

He's mumbling, throwing his head back as the ball goes wide.

Deuce again.

Image source, Reuters

Here we go. A Sock mistake brings up break point for Roger Federer.

This is it? No! Wide! The world number two slices his backhand into the tramlines.

Still Sock fights on but there's no let up.

The world number nine is going to have to save another break point now...

Jack Sock looks a little weary, short sleeves crumpled up around his shoulders and collar spread wide exposing a gold chain around his neck.

Trick shot! The American rushes into the net and plays a volley between his legs but Federer isn't laughing. He just bashes the next ball past him for a backhand winner.

We go to deuce. This could be the match right here.

Russell Fuller
BBC tennis correspondent on 5 live

Sock is playing very, very steadily.

Those in US tennis are quite excited about some of the younger players coming through and Jack Sock has been a bonus for them this year. He’s shown all-round improvement, his backhand is much better than it was.

He surprised himself by reaching these Finals and took advantage of some of the frailties of the leading names on the tour. It will be interesting to see if he can kick on.

I'm sorry but there is no better sight in sport than Roger Federer on song. He puts that last game behind him either a beautiful point featuring a thumped half-volley, a single-handed backhand and a forehand winner.

All eyes back on the Jack Sock service game now.

There wasn't much to smile about for Jack Sock in the first set, but this moment had both the American and the crowd amused.

Watch Roger Federer hit the tape as Jack Sock prepares to take his punishment here...

One to make a note of. On break point, Roger Federer misses a second serve return and that allows Jack Sock to stay alive.

And now at the perfect time the American's big serve returns to allow him to stay in front.

Sloppy from Federer. He could have had this all-but wrapped up there.

Image source, Reuters

Uh oh.

Here is the moment Jack Sock and his fans must have feared.

A slight drop in the accuracy of his serve and Federer is ready to pounce.

Two break points to Federer.

Tim Henman
Former British number one on BBC TV

For me, the history and tradition of the Grand Slams are the cornerstone of our sport and I don’t think they need to be tweaked. But other events on the tour, where they might struggle week in week out as matches take too long for the TV audience, by all means try the shorter formats. And this is an individual sport, so to bring in coaching I think takes it away from the players.

The problem for Jack Sock though is without the crunching start to the point on his serve, he can't get ahead in the rallies when Federer plays the first shot.

Fed makes the American look a little silly by playing the ball back behind him as he races across the baseline.

One we go in this set. Still on serve.

Image source, Getty Images

Bang, bang, bang. Jack Sock now rattles through a service game, whacking the ball down in the high 130s-mph.

He looks pleased with his start to this set and he should be. Federer hasn't had a look in.

Image source, EPA

Federer is finding his way into the net at any opportunity now, playing similarly to how he's racked up eight titles a little west of here at Wimbledon.

He shows lovely touch to get down low and play a cross-court drop volley that Sock can't retrieve.

Classy.

The big serve is now in motion for Jack Sock as he secures another service game comfortably. I fear that Roger Federer is just biding his time to pounce though.

The Swiss hasn't quite been at the top of his game in those first couple of games from the American.

Ever the perfectionist Roger Federer grumbles as he makes a rare error in this match but Jack Sock just hasn't quite been consistent enough to really apply the pressure.

On game point the American number one winds up a backhand winner but his radar is out and the ball flies wide.

Much better from Jack Sock.

The American wins the opening game of the second serve to love. He's got nothing to lose now right?

The American didn't even expect to be here this week, he was booked in for a round of golf at Augusta with fellow American tennis player John Isner.

Golf at Augusta or tennis against Roger Federer? It's a tough life.

Image source, PA

Right.

What can Jack Sock do to try and prevent what seems inevitable here?

Jack Sock can't afford a slack start to the second set like he did in the first.

Image source, Getty Images

Even the title this week will not be enough for Roger Federer to finish the year as world number one. That honour will go to Rafael Nadal for the first time since 2013.

But Nadal arrives here with injury issues, admitting his knee is "not perfect" after withdrawing from his match at the Paris Masters last week.

The Spaniard will get his Tour Finals campaign under way tomorrow against David Goffin.