LONDON • While Andy Murray is basking in the achievement of overhauling Novak Djokovic at the top of tennis' world rankings, the inquisition into the once-dominant Serb's slide has begun.

Djokovic has spent much of the past six months talking about his development as a human being but, if he has become a better person, it appears to have been at the expense of his game.

That has rarely been more clear than in last Sunday's 6-3, 6-4 defeat by Murray in the final of the ATP World Tour Finals, which guaranteed that the Scot will end this year as the world No. 1.

Many aspects of Djokovic's game were out of sorts during his 1hr 42min defeat, but none more than his error-riddled backhand.

Throughout his period of dominance, in which he has won 12 Grand Slam titles and held the top ranking for more than four years in three spells, his two-handed backhand was regarded as the prime reason for his supremacy. It set the standard for the rest of his game.

Because of his superb athleticism, he was able to get into the perfect, precise position to play the shot, staying low to strike balls down by his feet and accelerating his racket head through the ball.

It was his banker shot.

However, on Sunday, the flawless technique deserted him in his time of need and the effects were alarming.

He hit 30 unforced errors on Sunday, a massive rise on the 14 he made in last year's final - a 6-3, 6-4 victory over Roger Federer. Of those mistakes, 17 came off the hitherto reliable backhand.

Former British player Greg Rusedski, speaking on Sky Sports, believes a minute change in the execution of his backhand technique was crucial.

"I don't think his shot has changed but he used to sit on it and steer it through the court," Rusedski said.

"Against Murray he was pulling out of the shot a fraction quicker and the ball was consequently heading off wide.

"To me, it's most definitely a confidence thing. He didn't appear to have the self-belief in his shots."

Pat Cash, the 1987 Wimbledon champion, thought that Djokovic played a nervous match.

"He couldn't get his feet in exactly the right position and, three times in a row on his backhand, ended up with the ball too close to his body," the Australian said.

"He then repeatedly slid the ball wide and lost confidence in himself.

"I now really do wonder if Novak is losing his edge. The danger for him is if this continues into 2017."

Coach Marian Vajda told Serbian journalists that there is no crisis, insisting Djokovic's poor end to the season was a result of his exertions in winning four Grand Slam events in a row, between Wimbledon last year and Roland Garros in June.

"He put a lot of energy into this, and by the Paris Masters he was totally drained," Vajda said.

"For a while there was the problem, 'When you have won everything, how to find a motivation to continue?' After so many years and successes, it was natural, but Nole will return."

THE TIMES, LONDON