Stanislas Wawrinka "disappointed" by lack of energy in Novak Djokovic loss

Stanislas Wawrinka could not hide his disappointment at missing out on a spot in the final of the ATP World Tour Finals at the expense of Novak Djokovic at the weekend.

The Serb defeated the 28-year-old Swiss 6-3 6-3 on Sunday at The O2 to advance to the final of the competition to face Rafael Nadal.

"I had the feeling that I was playing good, hitting well the ball," Wawrinka told reporters. "But I think I don't have enough energy. Against him, that makes a big difference.

"I'm disappointed with myself because I had the feeling that I could have done something better, but I really think that I was not fresh enough to do something."

Wawrinka has beaten Djokovic just twice in their last 17 encounters.