Kevin Anderson says the pressure is off but wants to maintain his winning run tonight:

"I'm looking forward to playing Roger, it is always a great challenge taking him on on the court.

"It's a great opportunity, up against arguably the best player of all time.

"I feel like I've played two really good matches, so definitely excited to come back and play him."

Kevin Anderson is doing a few shuttle runs in the O2 corridor. Knees up, heels to bum, side to side. The full Sunday league repertoire.

The South African is already safely through to the last four on his ATP Finals debut.

Tim Henman
Former British number one on BBC TV

I wouldn't think Federer would use the word revenge but certainly having lost to Anderson and being two sets to love up and having match point then he'll want to win.

He lost his first match here, which was very unusual, but now the ball is in his court. He has to deliver.

Roger Federer doesn't need any added motivation to win tennis matches but, if he did, then he's got it tonight.

You might remember the last time these two met. A scorching summer's day at Wimbledon. Five sets.

Federer leading two sets to love, missing a match point in the third set. Anderson fighting back to win in over four hours.

A stonecold classic.

Image source, Getty Images

Put simply, it means Federer will reach the semi-finals if he wins a set against Anderson.

But even if he loses in two sets then the Swiss maestro can still progress with the South African.

How can that happen?

• If Federer wins five games in total if Anderson wins both sets in six games
• If Federer wins six games in total if Anderson wins one of the sets in seven

Got your head around it? Good.

If watching the news today has given you a headache then I hope you didn't read all the possible permutations for the season-ending tournament between the world's best male players.

There were 16 possible permutations in Group Lleyton Hewitt before today's afternoon match between Thiem and Kei Nishikori - and then some percentages to work out. It was like GCSE Maths all over again...

But Thiem's two-set win over Nishikori makes everything a lot simpler for everyone. Including Roger Federer...

Is there anything Federer can't wear with style? He arrived at the O2 wearing a beige duffle coat. The sort Paddington Bear had an endless supply of. And he still looks cool.

Image source, Getty Images

Hello! The O2 is one corner of London where the focus won't be on Brexit tonight.

And while there is still a possibility of Fedexit (doesn't quite have the same ring, does it?), the chances of the GOAT reaching the last four of the ATP Finals for the 15th time in 16 years look pretty likely.

Today always promised to be a complicated and uncertain day for all involved.

Both sides going at one another in London... attack, defence and counter-attack in the glare of the world's media... highs and lows with some casualties along the way...

An ever-evolving picture leaving the rest of us confused and angry...

And then Dominic Thiem won in straight sets to put a more-straightforward deal on the table.

Image source, Getty Images