Roger Federer opened his challenge for a seventh ATP Tour Finals crown in dominant fashion on Sunday with a 6-1 7-6 (7-0) victory over Canada’s Milos Raonic.

Federer last won the prestigious season-ending event at London’s O2 Arena in 2011 and the world No.2 looks in the mood to add another title to his collection.

In a powerful performance, the Swiss racked up 24 winners, avenging his loss to Raonic last month in the Paris Masters quarter-finals.

Earlier, Kei Nishikori made a dream start to his Tour Finals debut as the Japanese star clinched a surprise 6-4 6-4 victory over Andy Murray.

Nishikori, the first Asian singles player to qualify for the prestigious tournament, rose to the occasion with his first victory over Wimbledon winner Murray at the fourth attempt.

The 24-year-old had failed to win even a set in those losses to Murray, but the last came more than two years ago.

He took the game to Murray from the start and hit 20 winners in a 95-minute triumph that gives him a good chance of qualifying for the semi-finals from the same group as Federer and Raonic.

“Maybe in the beginning I was a little bit tight, but I started feeling better and the second set was almost perfect,” Nishikori said.

“I knew I had to be more aggressive than usual and that’s how I won. It’s my goal to go to the semi-final and final.”

With matches against 17-time grand slam champion Federer and in-form Raonic still to come, Murray admitted he faces a fight to make the last four.

“It’s harder to qualify when you lose your first match. That’s pretty obvious,” he said.

“I need to win my next two matches more than likely, and win them well if I want to go through.

“That’s going to be tricky because Milos played fantastic last week in Paris, and Roger always plays well at this event.”