London - Rafael Nadal lost to Robin Soderling for the second straight time, falling 6-4, 6-4 Monday in their opening round-robin match at the ATP World Tour Finals.

Soderling, who handed the Spaniard his first loss on clay at the French Open this year, powered his way through the Group B match by mixing a hard forehand with a solid backhand to keep Nadal running all over the court.

"He is a big player in this surface, so (it) is difficult," Nadal said. "I didn't play really bad. But in the important moments, I didn't have this calm, this necessary calm, to win these matches against the best players of the world."

In the late match, Novak Djokovic rallied from a poor start to beat Nikolay Davydenko 3-6, 6-4, 7-5 and move a step closer to the semifinals of the season-ending tournament for the top eight players in the world.

The second-ranked Nadal can still advance, but likely needs to win his two remaining group matches. He also has a chance to claim the year-end No. 1 ranking from Roger Federer, but Monday's loss hasn't helped.

"If you want to still talk about me (being) No. 1, I can, but I think is not the right moment. My level right now I think is not to be No. 1," Nadal said. "My level is to be still fighting and practicing hard to be ready as soon as possible to compete another time with equal conditions with everybody."

Soderling was only invited after Andy Roddick withdrew because of injury.

Today, four-time champion Federer will face Andy Murray and Juan Martin del Potro will play Fernando Verdasco.