Roger Federer qualifies for semi-finals of ATP Finals in London
Swiss beats Kevin Anderson 6-4 6-3 to top his group
South African Anderson already guaranteed place in last four
Dominic Thiem bt Kei Nishikori 6-1 6-4 earlier
Thiem & Nishikori eliminated from Tour Finals
Federer 6-4 3-3 Anderson*
Anderson hasn't managed to take a look at Federer's serve in this set yet. Nor has Roger at his.
Federer holds to 15 as Anderson drives a double-handed backhand long from his own baseline.
That was quite Aggie Radwanska, actually. Maybe he was paying homage to the former Wimbledon finalist, who announced yesterday she was retiring.
David Law
BBC Radio 5 live tennis commentator at the O2 in London
This is uplifting to see Federer playing this well. It was dispiriting to see Federer play so listlessly on the first day. You almost thought he was ill.
*Federer 6-4 2-3 Anderson
And hanging in there is exactly what Kevin Anderson does again.
The South African is nailing his first serves in this set, racking up a pair of aces on his way to another hold.
Image source, AFP
Leon Smith
GB Davis Cup captain on BBC Radio
Federer's footwork is looking good and he's being offensive in his game but Anderson can hang in there with his serve.
Federer 6-4 2-2 Anderson*
A bit of Jazzy Jeff and the Fresh Prince entertains the crowd at the changeover. But there's no 'Boom!' for Federer as he loses the first point on his serve.
The Swiss does shake the room though as a wonderfully-crafted point, turning defence into attack and finishing with a forehand volley.
Anderson goes long for 30-15 and then gets strings on a first serve from Fed but can't direct it to safety.
It's briefly 40-30, and I mean brief, because seconds later Federer lands a serve on a postage stamp out wide.
*Federer 6-4 1-2 Anderson
Another good response from Kevin Anderson. The South African moves 40-15 ahead and clinches another hold when Federer miscues a forehand long.
David Law
BBC Radio 5 live commentator
This is a different Federer to the one we saw at the beginning of the tournament.
He is expecting to dominate Anderson now.
Image source, Getty ImagesFederer 6-4 1-1 Anderson*
Federer's footwork is fancier than John Travolta's in Grease at the moment.
The Swiss is meeting everything that comes back into his side of the court at the moment, wrapping up a comfortable hold with a dink which even 6ft 8in Anderson can't reach with a stretched arm.
*Federer 6-4 0-1 Anderson
What Anderson needs is a tummy settler of a hold. And that's what he gets with a hefty second serve on game point.
Federer 6-4 0-0 Anderson*
Pressure off the shoulders of both men now. Which, you'd think, might spell more trouble for Kevin Anderson...
Dominic Thiem, meanwhile, has just called a cab to Heathrow Airport. He might see Kei Nishikori in the first-class departures lounge...
Federer 6-4 Anderson
Superb stuff from Federer. Anderson didn't do too much wrong from 40-0 down, apart from standing opposite the GOAT.
Federer is through to the semi-finals and now it is a straight winner-takes-all scrap for top spot in the group.
Finish top and you (probably) avoid Novak Djokovic...
Image source, Reuters*Federer 5-4 Anderson
Two of those chances quickly disappear down the drain, leaving Anderson starting at all or bust.
Federer pauses, looks towards his opponent, then effortlessly cracks down an ace out wide.
Deuce...
*Federer 5-4 Anderson
Leon Smith
GB Davis Cup captain on BBC Radio
Four breaks in a row from one of the most powerful servers in the world like Anderson and one of the most accomplished in Federer would be very unusual.
It's been entertaining though.
*Federer 5-4 Anderson
So here we are. Federer serving for the set - and a place in the ATP Finals semi-finals...
But wait! Federer double faults for 0-30 as both men continue to wobble on serve.
And then it is 0-40 when he races forward to meet a short ball but can't direct it to safety. Three break points to Anderson...
*Federer 5-4 Anderson
This set is starting to have more ups and downs than the Big Dipper.
Federer racks up three more break points as Anderson's serve continues to crumble under pressure.
Seven points in a row that the South African has now lost. Make that eight!
Federer keeps batting back the returns that Anderson throws at him, then glides into the net and breaks again with a beauty of a backhand volley.
Federer 4-4 Anderson*
Leon Smith
GB Davis Cup captain on BBC Radio
A couple of unusual decisions from Federer on serve but Anderson has this big reach and was able to capitalise.
It's been a high level in the first six games but there have been several unforced errors in the last two.
Clearly stress is affecting both players at the end of this set.
Federer 4-4 Anderson*
Kevin Anderson is starting to make a habit out of rewriting Roger Federer's scripts.
Suddenly the South African has a break point and levels the opening set when Federer pulls a forehand well wide.
Image source, PA*Federer 4-3 Anderson
Federer serving to back up the break - and, more importantly, put himself within touching distance of the last four.
It starts brightly with a 30-0 lead but then turns murky very quickly... out of nowhere Anderson fights back and forces deuce...
*Federer 4-3 Anderson
The first time this week that Anderson has lost his serve if I recall correctly...
*Federer 4-3 Anderson
Leon Smith
GB Davis Cup captain on BBC Radio
Anderson normally has a very reliable serve with the height he has and technically it's very good too but he didn't take his opportunity in the previous game and maybe he dwelt on that and lost his focus.
It's very unusual for Anderson to do that on his serve.