Roger Federer, who defeated Kei Nishikori in three sets at the ATP World Tour Finals, said afterward that he really enjoys seeing younger players rise. The 34-year-old remembered coming up the ranks himself.

"I loved the times before when I played my heroes, like [Pete] Sampras. Then other cool players I only knew from TV: [Tim] Henman, [Carlos] Moya, [Andre] Agassi—you name it, all these guys—Wayne Ferreira, [Richard] Krajicek. Next thing you know I'm playing doubles with those guys.

"It was different, exciting times, but really, really special to make it on the tour and be in the restaurant together with them. It was crazy cool. Then all of a sudden they're all gone and now you're the old guy. Now you have to inspire yourself in a new way."

Federer qualified for the semifinals in London even before his 7-5, 4-6, 6-4 win over Nishikori. The 25-year-old from Japan has yet to win an ATP Masters 1000 or a Grand Slam, but Federer likes his attitude.

"Kei is definitely one of those guys. It's amazing what he's able to produce on the court," Federer said. "Today was another showcase of that, how he's able to return second serves, staying on top of the baseline, drilling forehands and backhands up the line. It was impressive. I look forward to playing him hopefully more often in the future."