Roger Federer beats arch-rival Rafael Nadal to take ATP year-end title for fifth time in his stellar career

How sweet this must be for Roger Federer.

After being relegated to number 2 in the world by Rafael Nadal, the greatest player in the history of men’s tennis showed on Sunday that he still has plenty of fight left by beating Nadal at the ATP World Tour Finals.

Federer’s 6-3, 3-6, 6-1 victory was his eighth victory over Nadal in 22 career matches between these two remarkable champions. He and Nadal have combined to win 21 of the past 23 majors.

“You played unbelievable all during the week,” Nadal said to Federer on court after the match. “So well done for everything.”

Federer, 29, reflected on his win and his future at the post-match press conference: “As long as I can, as long as I’m healthy, eager, motivated, which I clearly am, [I will continue to play]. I’ve played 10 full seasons. Nine of them I made the World Tour Finals, so I’ve always had long and exhausting seasons. But I seem to enjoy it. I take pleasure out of travelling the world, playing against the best, challenging myself.

“So it’s been an amazing career for myself. At the moment I have no plans at all of stopping, quitting, whatever you want to call it. I hope I can play for many more years to come. It’s a goal anyway. I think it’s possible.”

The year-end ATP tournament is considered one of the sport’s most prestigious outside tennis’s four grand slam championships and Federer had to get past three of his top rivals to win. He beat fourth-ranked Andy Murray in the round-robin portion then third-ranked Novak Djokovic in the semifinals and then Nadal in the final.

For Federer, it was his fifth season-ending title. He has won Wimbledon six times, the US Open five times, the Australian Open four times and the French Open once.

All that is missing in his collection is the Olympic Gold Medal in singles (Federer won the gold in doubles at the 2008 Olympics).

Nadal has never won the year-end title and was playing in the final for the first time. He was 2010′s dominant player winning the French Open for the fifth time, Wimbledon for the second time and the US Open for the first time. He has also won the Australian Open once and was the 2008 Olympic Gold Medalist in singles.

Federer’s win is good news for tennis fans because it signals that the Swiss superstar will be eager and in top form in 2011 after a often disappointing 2010. He started the year by winning the Australian Open then did not win another title until the summer.

His partnership with new coach Paul Annacone is clearly paying dividends as Federer has tweaked his game by shortening points and playing a more offensive game.

He finishes the year with five titles and posted a 37-4 record since hiring Annacone after Wimbledon.