LONDON (AP) -- Experience prevailed over youth as Roger Federer tamed Milos Raonic 6-1, 7-6 (0) in his opening round-robin match at the ATP Finals Sunday after Kei Nishikori started his maiden campaign at the season-ending tournament with a win.
Federer, the most successful player at the elite championship, started brilliantly against the 23-year-old Raonic - the youngest player of the eight-man field - then withstood his assaults in the second set.
The 17-time Grand Slam champion, chasing a seventh title, saved all four break points he faced to avenge his loss to the big-serving Canadian in the quarterfinals of the Paris Masters last week.
''Thankfully he didn't play quite so well, like he did in Paris maybe,'' the second-seeded Federer said. ''He gave me a few shots here and there, especially at the beginning of the breaker. I think those were crucial. I was happy to bring it home because it was very close at the end of the second.''
Raonic did not play as freely as he did in the French capital while Federer, who is ten years older than Raonic, returned much better to break his opponent twice in the first set.
Raonic hit 10 aces to Federer's five and gave the Swiss a tougher challenge in the second set as both players held until the tiebreak after Federer saved a set point with a service winner in the 12th game.
The Canadian, one of the three debutants at the O2, then played a terrible tiebreak laced with unforced errors.
''It's obviously disappointing, very disappointing actually, the way I finished that second set off,'' said Raonic. ''He was a lot more consistent on his return games. In Paris, I'd get free points when I hit aces, but today the big difference was when he would get his racket on the ball, he would make me play all the time.''
Earlier, Nishikori started his campaign with a 6-4, 6-4 win over home favorite Andy Murray, who is now facing an uphill task to reach the elite tournament's semifinals. After the round-robin stage, the top two finishers in each group will advance.
''Obviously now I need to win my next two matches more than likely, and win them well if I want to go through,'' said Murray, who missed last year's tournament after undergoing surgery on his back. ''That's going to be tricky because Milos obviously played fantastic last week in Paris, and Roger always plays well at this event. So I'm definitely going to have to play better if I want to get through.''
The fourth-seeded Nishikori - the first Asian player to qualify for the year-end championship - secured important points in the tough Group B before taking on Federer on Tuesday.
Murray, who had never lost a set to the Japanese newcomer in their three previous matches, only sealed his spot at the season finale last week in Paris following an impressive run that saw him win 20 of his previous 23 matches.
Against Nishikori, the former Wimbledon champion never looked capable of turning the match around. He dismissed the idea that fatigue finally took its toll on him.
''I felt OK on the court today,'' he said. ''I don't think that was the reason why I lost the match.''
The Scot secured the first break in the fifth game after taking advantage of his opponent's unforced errors but could not hold his next serve after hitting two double-faults.
Nishikori did not serve well either, hitting eight double-faults and averaging a low first-serve percentage of 46. But Murray's struggles were even worse, winning only seven points on his second serve.
After a cautious start, Nishikori pushed Murray into long rallies before overwhelming him with powerful groundstrokes. Pegged back well behind his baseline, Murray saved one set point with a crosscourt forehand that Nishikori could not return but fluffed a backhand drop shot on the next one.
The U.S. Open runner-up continued at the same pace in the second set and broke for a 2-0 lead after leaving Murray stranded on the baseline with a fine drop shot. Murray fought hard to save three break points in the fourth game to stay in the match and a series of errors from Nishikori in the seventh game helped him to break back.
Murray leveled at 4-4 but could not build on the momentum as Nishikori converted his first match point in the 10th game when Murray dropped his serve for the fourth time following three consecutive backhand errors.
''The second set was almost perfect,'' said Nishikori. ''I knew he is very consistent from the baseline so I knew I had to be more aggressive than usual and that's how I won today.''
Two-time defending champion Novak Djokovic is playing his opening match in Group A against Marin Cilic on Monday after Stan Wawrinka takes on Tomas Berdych.