Postpublished at 14:09 Greenwich Mean Time 21 November 2015
Djokovic v Nadal
Summary
Roger Federer beats Stan Wawrinka 7-5 6-3
Federer v Novak Djokovic in Sunday's final (18:00 GMT)
Djokovic beat Rafael Nadal 6-3 6-3
Postpublished at 14:09 Greenwich Mean Time 21 November 2015
Knock-up underwaypublished at 14:07
Djokovic v Nadal
Image source, AFPThe stadium emcee raps his vocal cords around Rafa Nadal's vowels with relish as he announces the players' arrival on court.
The players unwrap their bats in near darkness as the house lights are kept off and the dance music keeps pumping.
It is like a sweaty spinning class at the O2.
To the net. Rafa bouncing, Novak stretching hamstrings. Umpire Mohamed Lahyani issues final instructions and competition winner 'Sharon' flips the coin and poses for photos.
Knock-up under way.
BBC coveragepublished at 14:02
Djokovic v Nadal
BBC OneQuick, everyone over to BBC One.
A lovely sepia start to the television coverage, full of clenched fists and grimaces from past meetings between Novak Djokovic and Rafael Nadal.
Down to business and Andrew Castle has ticked the "era-defining rivalry" soundbite off your bingo card.
Get involved via the play icon at the top of this page.
Nadal the one to watch in 2016published at 13:59 Greenwich Mean Time 21 November 2015
Piers Newbery
BBC Sport at the O2 Arena in London
Image source, Rex Features"He showed what's to come in 2016, in my opinion.With some time to practise and reassess his game, he's going to be tough to beat in Australia. I believe that." Nadal's resurgence has not gone unnoticed by the rest of the field and Roger Federer is predicting big things from his great rival next year. Nadal himself has been in an unusually cheerful mood all week in London and is planning an intensive off-season, even by his standards. "I don't deserve a vacation," he joked. We think.
Swiss rolepublished at 13:57
Image source, GettyThis is the day's first semi-final of course.
The evening session, appropriately enough for an arena set in the heart of London's financial engineroom, is an all Swiss affair.
Tennis' Dorian Gray Roger Federer takes on the majestic backhand that comes attached to Stan Wawrinka.
The first serve crashes down in that one shortly after 20:00 GMT.
Skill and crossed racquetspublished at 13:51
Piers Newbery
BBC Sport at the O2 Arena in London
Image source, Getty ImagesIt's an icily cold day on the North Greenwich Peninsula, a place where the corpses of pirates were once hung in cages to warn off others. Now they play tennis in a giant tent, which is a much better idea. Semi-finals day has provided real drama here over the years, from Murray and Nadal's epic in 2010 to Federer and Wawrinka's falling out last year. There are 17,000 spectators now making their way through security fully expecting another thriller this afternoon.
Head to headpublished at 13:47
Djokovic v Nadal
Image source, Getty ImagesSince then Rafa has cut his hair, Novak has cut out gluten and one of the great rivalries in modern tennis has blossomed.
There have been 45 matches between the pair, with Nadal narrowly ahead 23 to 22 on the countback.
And what gems there are in that long list.
Rafael Nadal winning out in a five-set epic in the French Open semi-finals in 2013.
Novak Djokovic coming through in five hours and 53 minutes in a pulsating Australian Open final in 2012.
What awaits us this afternoon as they go head to head for a place in the World Tour Finals?
Back in the daypublished at 13:45
Djokovic v Nadal
Image source, Getty ImagesThe first Tour meeting between Novak Djokovic and Rafael Nadal was back in June 2006 when Tim Henman and Greg Rusedski were still knocking around in the first week of the French Open.
Nadal and Djokovic met in the quarter-finals at Roland Garros with the Spaniard prevailing via a retirement when 6-4 6-4 up.
It did not feel like the start of something.