Roger Federer of Switzerland
Roger Federer of Switzerland wipes his face during his men's singles tennis match against Milos Raonic of Canada at the ATP World Tour Finals at the O2 Arena in London November 9, 2014. Reuters

Roger Federer and Kei Nishikori beat separate opponents on Monday to open the action at the season-ending ATP World Tour Finals at the O2 Arena in London.

Nishikori from Japan defeated Andy Murray of Great Britain in straight sets, 6-4, 6-4 to open is first-ever campaign in the tennis season finale. Federer meanwhile dominated Milos Raonic of Canada early winning the first set, 6-1 before holding off the comeback bid in the second winning the second set via tiebreak, 7-6 (0).

Nishikori finished off Murray in just a little over one hour and a half surviving 8 double faults of his own and 7 aces from the British number one.

"I was a little bit tight in the beginning, but I started feeling a little more confident in especially second set," Nishikori in the tournament’s official website. "I was very, very solid… I was a little bit surprised at how I played on the court: very confident. I'm looking forward to play the next match.

What worked for Nishikori was breaking Murray’s serve in key moments in the match— the Japanese was 4-of-8 on break points while Murray was just 2-of-6.

Meanwhile, Federer was dominant very early against Raonic, who even had 5 aces in the opening set. The Swiss Maestro broke Raonic twice in the first set to rattle the Canadian early. Federer won the match after 1 hour and 28 minutes. Like Nishikori, Raonic was also making his debut in the ATP World Tour Finals.

"I think I played really well for probably one and a half sets," Federer said also in the ATP World Tour Finals website. "It was good to get off to a good start like I did against him at Cincinnati and Wimbledon. I broke in the first game and sort of never looked back.”

Group stage action of the 2014 ATP World Tour Finals continue on Tuesday (Australian time) with Stanislas Wawrinka (Switzerland) taking on Tomas Berdych (Czech Republic) starting at 1:00 am and Novak Djokovic (Serbia) facing Maric Cilic (Croatia) at 7:00 am.