The Barclays ATP World Tour Finals is underway in London, with all eyes on Rafael Nadal and Novak Djokovic in their quest for the No. 1 ranking of 2013.

Both Nadal and Djokovic are idle on Monday, as they prepare to face their respective group opponents in a round robin. In Group A, Nadal will go head-to-head with Tomas Berdych, David Ferrer, and Stanislas Wawrinka. Djokovic will face Roger Federer, Richard Gasquet, and Juan Martin del Potro in Group B. There is a great deal of familiarity between the players, as all eight made the quarterfinals at the Paris Masters, with Djokovic edging Ferrer in the final on Sunday, 7-5 7-5.

Djokovic still has a slim chance of finishing as the top player in the world. Nadal has 12,030 points, while Djokovic has 10,610. Ferrer is a very distant third at 5,800.

In order for Djokovic to take the top spot, he would have to win the tournament without losing a match, and also earn the 300 ranking points from the Davis Cup final. Nadal can hold off Djokovic by simply winning two round-robin matches.

Nadal could have clinched the year-end No. 1 ranking in Paris, but fell to Ferrer on Saturday. After the 6-3 7-5 win, Ferrer said that he may have played the best match of his season.

Djokovic has been on a hot streak, with a 17-0 record since the U.S. Open. But Nadal seems unlikely to falter despite his recent loss to Ferrer. It would take exceptional efforts from Berdych and Wawrinka to unseat Nadal. Djokovic is aware that he faces a daunting challenge.

“No. 1 does not depend on me only. It depends on Rafa,” said Djokovic. “I know there are small chances. If I finish No. 1 in the world this year, it would be an incredible achievement.”

Nadal has had some problems with this tournament, with a finals appearance in 2010 as his best result. The 27-year-old has also only won one indoor tournament in his career, and is less comfortable on hard court than clay. 

He looked dominant against Gasquet last week, but perhaps Ferrer exposed some flaws in Nadal’s game at this point of the season. Nadal had to rest in October in preparation for Paris and London, and could be suffering from fatigue after an arduous 2013.

Perhaps the best evidence for Nadal to finish No. 1 is his competitive drive. He rarely suffers through losing streaks, and enters the tournament with a chip on his shoulder. Losing to Ferrer and knowing Djokovic is gunning for the No. 1 ranking should serve as added incentive for the Spaniard to play at his highest level.

An IB Times staff reporter contributed to this report.