Roger Federer and Kei Nishikori contest the first match of the last set of round robin matches at the ATP World Tour Finals.
Where to watch
Federer vs Nishikori is live on Sky Sports 1HD and BBC Radio Five Live sports extra at 2pm.
Kei Nishikori must beat Roger Federer and hope results go his way to retain his interest in the ATP World Tour Finals. The Japan number one defeated Tomas Berdych to stay alive in the competition but anything less than a win over the already qualified Federer will see him crash out at the round robin stage.
There is no margin for error for Nishikori on day five of the tournament with victory required to ensure he remains in contention going into the final match of the Stan Smith group. Should the former US Open finalist prevail by any scoreline, then victory for Tomas Berdych will see him progress and as the group winner. Anything less, and the 25-year-old will miss out on a second straight semi-final appearance.
The scenario is much more simple for Federer, who cruised through to the semi-final with a straight sets win over the world number one. Victory will leave the 17-time grand slam champion with a 100% record and top of the group, but even a loss in his third round robin match could still see him qualify top.
Only a defeat for Federer coupled by victory for Berdych against Djokovic - which would send the three-time defending champion packing - would see him finish second to final round robin opponent Nishikori. Federer's route to the final is hardly likely to be easy though, with Andy Murray or Rafael Nadal potentially in wait.
What the players say
Roger Federer: "I thought he [Nishikori] was fast, number one. He has to be for his height. He needs to be fast. If you don't have the speed, being his size, it's going to be tough. But he had it, natural speed, very coordinated.
Then he had the power, as well. For a smaller guy, it's not so easy for him to do. He finds it very easy to generate a lot of power on the backhand, finds great angles on the backhand, and can redirect up the line almost better than anybody right now in the game.
"He showed his talents very quickly and very early. It just took him awhile because of his injuries to really, really break through. Now he's there and one of the best players."
Kei Nishikori: "It's going to be really big challenge for me to play Roger. It's always excited. It's going to be really important match for both of us.
"I mean, it's going to depend tonight's match. But I have to win the next match to qualify the group. So I try to recover well today and tomorrow, and I will get good tactics ready and try to play another good match.
"He's still improving his-self, playing great tennis even he's 34. He doesn't look old for me. It's a great honour to play Roger. Yeah, I actually never think about age on the court."
Betting odds (source William Hill):
Roger Federer 1/6 vs 4/1 Kei Nishikori
Head-to-head record: Federer 3-2 Nishikori. Last match ATP World Tour Finals (hard) Federer bt Nishikori 6-3 6-2
Previous meetings at the ATP World Tour Finals: Federer 1-0 Nishikori. Last match Federer bt Nishikori 6-3 6-2