World number one Novak Djokovic "wasn't very satisfied" with his performance during his opening ATP World Tour Finals match against Tomas Berdych yesterday evening.

The Serbian fought back from one set down to claim maximum points from the encounter.

Despite being disappointed with his display, Djokovic did admit that he was happy with the victory.

"It was the toughest match probably since the US Open," said the 24-year-old. "I mean, I wasn't very satisfied with my performance tonight. I know I wasn't playing on top of my game. But a win is a win in the end."

Djokovic will take on Spain's David Ferrer in his second match on Wednesday.