By Erin Bruehl, USTA.com

The ATP Tour season comes to a close next week with the eight top singles players and eight top doubles teams competing in the season-ending Barclays ATP World Tour Finals in London starting Sunday, November 22 and running through November 29.

The players are split into two groups of four players (or teams) each for the opening round robin tournament with the players and teams with the two best records from each group advancing to the semifinals. Competing in Group A in singles are Roger Federer, Andy Murray, Juan Martin del Potro and Fernando Verdasco. Group B consists of Rafael Nadal, defending champion Novak Djokovic, Nikolay Davydenko and Robin Soderling.

And now here is a look at each of the competitors:

Roger Federer: The world No. 1 is a four-time champion here at the season-ending tournament, however it is possible he could lose his top ranking and the 2009 ATP World Tour Champion title to Nadal, depending on how each perform in London. Winning the title in London would cap a remarkable year for Federer, which saw him complete the career Grand Slam with the title at Roland Garros, set the all-time Grand Slam record with his 15th major title at Wimbledon and reclaim the top spot in the rankings. Since his shocking five-set loss in the US Open final to del Potro, however, Federer has played just two ATP tournaments – losing in the final of Basel to Djokovic and suffering an upset loss to Julien Benneteau in the first round of the Paris Masters. But throughout his career the mighty Swiss has performed extremely well at the season finale with an exceptional 27-5 record.

Rafael Nadal: After a great start to the season with his first Australian Open title, Nadal struggled with knee injuries throughout the second half of 2009, forcing him out of Wimbledon, causing an early exit from Roland Garros and he relinquished his top spot in the rankings. However, a great performance in London could still land him atop the world rankings as he is currently 945 points behind Federer. He has also performed well since the US Open semifinal loss to del Potro, reaching the Shanghai Masters final and the semifinals in Paris before falling to Djokovic. Nadal could also reach another milestone in London – he is just one win away for the 400th match win of his career. He starts the competition against Soderling, who gave the Spaniard his first career loss at Roland Garros this year in the fourth round.

Novak Djokovic: Djokovic, the world No. 3, is the defending champion here and has been on a recent hot streak, winning back-to-back titles at Basel and the Paris Masters in early November. He defeated amongst others, Nadal, Federer and Soderling along the way to winning those two titles, including upsetting Federer as the hometown favorite in Basel. In London, his first match will be against Davydenko, who is one of the few players Djokovic has lost to in recent weeks, in three sets in the semifinals of the Shanghai Masters in October. It has been a great close to what was a so-so start and middle of the season for Djokovic, who did not advance past the quarterfinals in a Grand Slam until reaching the semifinals of the US Open this year and dipped to No. 4 in the world at one point. Since a great semifinal in New York against Federer, however, the Serb seems to one of the few players playing his best at the end of a long season.

Andy Murray: The 22-year-old Scot has had the best season of his career in 2009, winning six titles to lead the ATP Tour and at one point jumped up to No. 2 in the world rankings (he now sits at No. 4). His maiden Grand Slam title was not in the cards this year, however, and he failed to reach any of the major finals including two fourth round exits at the Australian Open and US Open. He did win a few Masters Series titles in Miami and Montreal and post-US Open won the title in Valencia in early November. With the season-ending tournament moving to London this year from Shanghai, Murray is likely to have the hometown crowd behind him as a huge X-factor. His first match is against del Potro, against whom he is 4-1.

Juan Martin del Potro: Amongst the talented young players on the ATP Tour, it was del Potro who made the biggest breakthrough this year and won his first Grand Slam title at the 2009 US Open in a dramatic come-from-behind five set victory over Federer. The Argentine is still just 21 years old and possesses a dominating serve and power game, which will likely only keep him moving up the world rankings from his current spot of No. 5. Just like Federer, however, del Potro has played sparsely since New York, entering just three tournaments. He lost to Edouard Roger-Vasselin, then ranked No. 189 in the world, in straight sets in Tokyo; then retired in his opening match in Shanghai and retired in the quarterfinals in Paris while trailing 0-4 to Radek Stepanek. Does del Potro have enough gas left in the tank this year to win in London?

Nikolay Davydenko: Davydenko was slowed with injuries early in 2009 that kept him out of action for a few months but rebounded to have a solid season, winning four titles. Since the US Open, where he lost in the round of 16 to Soderling, Davydenko won the title in Kuala Lumpur just a few weeks later where he defeated both Soderling and Verdasco and won the Shanghai Masters with victories over Djokovic and Nadal – who are both in his round robin group - before most recently losing in the round of 16 in Paris. Perhaps his early season lay-off has left Davydenko fresher than some of his opponents but will it be enough to capture the crown in London?

Fernando Verdasco: The opening round robin pairings did not bode well for Verdasco, who is 0-3 in his career against first opponent Federer. They two last met in the quarterfinals of Indian Wells this year, which was a straight sets win for Federer. It has been a breakout season as a whole for the 26-year-old Spaniard as he reached the semifinals of the Australian Open, falling in a tight five sets to Nadal and performed consistently well all season despite winning just one title. He reached his career high ranking of No. 7 in the world and is now currently No. 8. At the US Open, he lost in the quarterfinals in four sets to Djokovic and then reached the final in Kuala Lumpur. He has played five tournaments since the US Open, most recently losing in the round of 16 in Paris and the semifinals of Valencia to round robin mate Murray.

Robin Soderling: Soderling established himself as a top contender on the ATP Tour this season and etched his place in the history books as the first man ever to defeat Rafael Nadal at Roland Garros. At Roland Garros he went on to reach the final, his first major final appearance, where he then lost to Federer. This will be Soderling’s first career appearance in the season-ending championships, earning a spot as an alternate when Andy Roddick withdrew with a knee injury. And Soderling proved he was not a one-time wonder, reaching the round of 16 at Wimbledon, the quarterfinals of the US Open and will end the year in the top ten for the first time in his career.

In the doubles competition, Daniel Nestor and Nenad Zimonjic are the defending champions and the No. 1 seeds. The No. 2 team is Bob and Mike Bryan, who is 830 points behind Nestor and Zimonjic in the competition for the ATP World Tour Champions title. Rounding out the rest of the competitors are No. 3 Mahesh Bhupathi and Mark Knowles; the 2009 US Open champions Lukas Dlouhy and Leander Paes at No. 4; No. 5 Frantisek Cermak and Michal Mertinak; No. 6 Lukasz Kubot and Oliver Marach; No. 7 Max Mirnyi and Andy Ram; and No. 8 Mariusz Fyrstenberg and Marcin Matkowski.