Roger Federer moved closer to the semi-finals. Reuters

Roger Federer produced another masterly display to beat Japan's Kei Nishikori 6-3 6-2 and move a step closer to the semi-finals at the ATP World Tour Finals on Tuesday.

The six-times former champion was at his imperious best to subdue the 24-year-old U.S. Open runner-up and will reach the last four should Canada's Milos Raonic defeat Andy Murray in the day's other Group B match.

Although this year's tournament is still to witness a three-set match, the entertainment served up by world number two Federer and Asian trailblazer Nishikori kept the capacity O2 crowd enthralled for one hour and nine minutes.

Federer clearly enjoyed it too.

"I was expecting a very difficult match," the 17-times grand slam champion said on court, to cheers from a vocal Swiss contingent complete with cowbells.

"I've know him since he was 17 years old and always thought he was a great talent and he's going to have a great future. I'm very pleased with the way I played."

The 33-year-old Federer, who can still knock Novak Djokovic off the top of the rankings before the end of the year, fought off two break points in the third game, one with an ace, and broke himself a game later with a flowing forehand pass.

That was enough for the Swiss maestro to secure the opener and the quality of his play pressured Nishikori into several errors on the backhand side at the same stage of the second set as he forged further into the distance.

There were flashes of inspiration by Nishikori, a graceful top-spin lob here, a sweetly-struck backhand pass there, but he lacked the authority he showed in convincingly beating home favorite Murray on Sunday.

Federer, who began his record 13th appearance at the ATP Tour Finals by subduing Raonic in straight sets, has only once failed to survive the group stage and looks poised to take center stage again at the weekend.

His final match will be against Murray who could already be eliminated should he lose to Raonic later.

(By Martyn Herman; Editing by Ed Osmond)