London, England -- (Sports Network) - Novak Djokovic rallied to beat Nikolay Davydenko in the second round-robin match of Group B play Monday at the season-ending ATP World Tour Finals.

The Serbian Djokovic, the reigning winner of this event, dropped the first set before taking a 3-6, 6-4, 7-5 win in a match that lasted nearly three hours.

The victory kept Djokovic rolling, as he has won his last two tournaments and three of his last four. The only interruption of his late-season run came in October against Davydenko, who beat Djokovic in the semifinal in Shanghai before winning the event.

In the first round-robin match of Group B, Robin Soderling continued his recent success against Rafael Nadal, posting a straight-set triumph over the Spaniard.

Soderling, who gained entry into the tournament as the first alternate when American Andy Roddick withdrew because of a left knee injury, notched a 6-4, 6-4 victory.

Nadal entered this match with revenge on his mind. Soderling stunned the world's No. 2 ranked player in the fourth round at this year's French Open, denying Nadal a chance to secure a fifth straight title.

On Monday, the Swede took the first three games in the opening set before Nadal rallied and pulled even at 3-3. Soderling then broke Nadal's serve to capture the first set. He went on to win three of the final four games in the second set.