Updated

London, England (SportsNetwork.com) - Kei Nishikori pulled off a mild surprise to start the ATP World Tour Finals on Sunday, beating Andy Murray in front of his home crowd in straight sets.

Nishikori kicked off Group B play at the O2 Arena with a 6-4, 6-4 victory, beating Murray for the first time in four all-time tries. Murray had never lost a set to Nishikori, but the two hadn't played since the start of the 2013 season in Brisbane.

The 24-year-old native of Japan had a banner 2014 season to qualify for the season-ending tournament for the first time, winning four titles with two other runner-up finishes. He also reached his first Grand Slam final, falling to Marin Cilic in the U.S. Open title match two months ago.

Murray grabbed a 3-2 lead Sunday in the first set after a Nishikori double fault, but the Scot was broken twice and dropped the first set. Nishikori broke again early in the second before Murray broke back to pull within 3-4, but Nishikori broke again in the 10th game to secure the victory.

It's the seventh straight ATP World Tour finals appearance for Murray, who won three titles in six events after the U.S. Open to qualify for the exclusive eight-man field.

Sunday's second Group B match will feature Roger Federer against Milos Raonic. The two met just eight days ago in the quarterfinals of the Paris Masters, with Raonic pulling off a straight-set win.

Round-robin action will be staged through Friday, followed by the semifinals on Saturday and lucrative final on Sunday.

Group A features top-ranked Novak Djokovic, the two-time reigning London champion who is in prime position to finish as the year-end No. 1 after his victory last Sunday in Paris. Cilic, Australian Open champion Stan Wawrinka and Tomas Berdych are also in Group A.

Federer has an outside chance of capturing the year-end top ranking. He and Djokovic are the only former champs in this year's Finals field. Former No. 1 Rafael Nadal is skipping this event after undergoing surgery to remove his appendix.