Nov. 20 (Bloomberg) -- Roger Federer is three wins away from finishing the season as the No. 1 in men’s tennis for the fifth time in six years.

Winning all his opening group matches at next week’s season-ending ATP World Tour Finals in London would mean the 28- year-old Swiss can’t be passed by Rafael Nadal.

The Tour finals, held Nov. 22 through 29 at the O2 arena in southeast London, are the culmination of the tennis season for the top eight singles and doubles players. U.S. Davis Cup captain Patrick McEnroe is picking Federer to win.

“He thrives in that kind of environment where he knows he’s playing against the best,” McEnroe said in an interview.

Federer is seeking to join Ivan Lendl as the only men to hold, lose and re-gain the No. 1 ranking at the end of the season. He finished the year in the top spot from 2004 through 2007 before his streak was ended by Nadal last year.

An undefeated champion may win as much as $1.6 million and gain a maximum 1,500 ranking points. Federer, ranked No. 1, and Nadal, No. 2, are only 945 points apart entering the tournament. No one else can claim the season-ending No. 1 ranking.

If Nadal wins all his group stage matches, wins his semi- final but loses the final he will earn 1,000 points. If that happens, Federer would need only to win one round-robin match to beat out Nadal for the top spot. If Federer doesn’t make the championship match, or win all three of his group stage matches, then Nadal could end the year as No. 1 as long as he finishes the tournament undefeated.

Federer has a 28-5 record at the finals with four titles, three more than the rest of the field combined. Nadal has a 4-4 record and made the semifinals in 2006 and 2007, losing both times to Federer, the eventual champion.

Injuries forced Nadal, a 23-year-old Spaniard, out of the finals in 2005 and last year.

Impossible

Nadal, whose season was marred by knee tendonitis that prevented him from defending his Wimbledon title, said he isn’t focused on regaining the top spot he lost to Federer after the grass-court Grand Slam in London in July.

“That is stupid talk right now,” Nadal said at a news conference last week at the BNP Paribas Masters in Paris, where he was ousted in the semifinals by third-ranked Novak Djokovic. “No. 1, I think, is almost impossible, no?”

The ATP World Tour Finals will be played in a round-robin format, with eight players divided into two groups. Each will face the three others in the section, with the top two in each half moving into the knockout semifinals.

Federer is the top seed in Group A, where he’ll face fourth-ranked Andy Murray of Britain, U.S. Open champion Juan Martin Del Potro of Argentina and Australian Open semifinalist Fernando Verdasco of Spain.

No Easy Matches

In Group B, top-seeded Nadal will play Djokovic, the defending champion from Serbia; 2008 runner-up Nikolay Davydenko of Russia; and French Open runner-up Robin Soderling of Sweden.

“Federer is the best in the world, Del Potro has won the U.S. Open and Verdasco has just had his best season to date -- there are no easy matches regardless of what group you’re in,” Murray said on his Web site.

There are questions about Federer’s thirst for another title after a season in which he won his first French Open, took a record-breaking 15th major title at Wimbledon and became the father of twin girls with his wife, Mirka.

“It all depends on how long he wants to play,” Paul Annacone, the former coach of 14-time Grand Slam winner Pete Sampras, said in an interview. “Most of those guys, at the end of their careers, it becomes more of a mental drain.”

Following his triumph at Wimbledon, Federer’s five-year run of U.S. Open titles was ended by Del Potro in September. He decided not to play tournaments in Asia in the fall, citing a “physically challenging year.”

Chances

After his break, he lost to Djokovic in the final of a tournament in his hometown of Basel, Switzerland, after winning the event three straight times. The next week, Federer lost his first match in Paris against unseeded Frenchman Julien Benneteau.

“I definitely had chances. I missed them,” Federer said at a news conference after his defeat. “Seems to happen a bit to me now, looking back at the Basel final or the U.S. Open final. I just have to make sure I don’t let chances go by like this all the time.”

Competitors have started to catch up with Federer, McEnroe said.

“He’s never going to dominate the way he did for a four- year stretch when he was winning 10, 12 tournaments a year and only losing four or five times,” the Davis Cup captain said. “Still, he’s proved by winning two majors, and reaching the final of two others, that he’s still the man to beat.”

One bad loss isn’t going to chance things, Federer said.

“Pressure is long gone since the French Open and other great victories I’ve had,” he said. “I hope I can make a good run, because I really feel like I have some good tennis left in me.”

To contact the reporter on this story: Danielle Rossingh at the London sports desk at drossingh@bloomberg.net

Last Updated: November 20, 2009 05:35 EST