Kei Nishikori
Kei Nishikori beat Andy Murray 6-4, 6-4.Reuters

World No. 5 Kei Nishikori of Japan beat British number one Andy Murray while six-time former champion Roger Federer avenged his recent loss to Milos Raonic of Canada in Paris in their Group B matches of the opening day's competition at the ATP World Tour Finals here.

Second seed Federer improved to a 45-11 record at the season finale with a 6-1, 7-6 (0) victory on Sunday over the seventh-seeded Raonic, who was making his debut at the tournament, reports Xinhua.

Federer was at his aggressive best losing just four of his service points to clinch the 25-minute set. Six of his eight winners came from his forehand while Raonic hit five aces.

The 33-year-old Federer has won the ATP World Tour Finals a record six times in three different cities.

Earlier, Nishikori, the first Asian player in history to make the year-ending event, demolished last year's Wimbledon champion 6-4, 6-4 in one hour and 35 minutes.

It was the Japanese player's first victory in his fourth meeting against Murray.