Novak Djokovic of Serbia celebrates after defeating Roger Federer of Switzerland in their men's singles tennis match at the ATP World Tour Finals at the O2 Arena in London, Nov 5, 2013. [Photo/Agencies]

LONDON - Roger Federer showed flashes of his best but Novak Djokovic exposed the Swiss maestro's fading powers with a three-set victory at the ATP World Tour Finals on Tuesday.

World number two Djokovic, at 26 six years Federer's junior, briefly looked in trouble midway through an absorbing Group B opener but eventually surged to a 6-4 6-7(2) 6-2 win in front of another sell-out crowd at the O2 Arena.

Djokovic's win, his 18th in a row since losing to Rafa Nadal in the US Open final, was his second in four days over Federer and kept alive his slender hopes of toppling the Spaniard from the top of the world rankings.

Rafael Nadal of Spain celebrates winning his men's singles tennis match against compatriot David Ferrer at the ATP World Tour Finals at the O2 Arena in London, Nov 5, 2013. [Photo/Agencies]

In the day's Group A match, Nadal crushed compatriot David Ferrer 6-3 6-2 and will seal the year-end No 1 ranking for the third time in his stellar career if he beats Swiss Stanislas Wawrinka on Wednesday.

Three days after losing to Ferrer in the Paris Masters semifinals, Nadal resumed his customary dominance over his compatriot with a victory that will not live long in the memory.

"I played with a little bit more calm than the other day," Nadal, who is trying to win the only major prize to elude him, told reporters after his first match at the venue since 2011 after he missed last year through injury.

"Last year was a big miss for me. Even if I was not able to play my best a lot of times here, I really have great feelings every time I have the chance to play in this stadium."

Nadal was gifted half the points he won in unforced errors by the unusually profligate Ferrer, who admitted it had been a "bad day".

Djokovic, on the other hand, was made to work hard against old adversary Federer.

With the pre-match music blasting around the steep stands and the players emerging on to a darkened court accompanied by smoke and lights the stage seemed set for some fireworks on the day Britain marks Guy Fawkes night.

However, the 31st clash between the two never quite reached a crescendo as Federer showed he is struggling to maintain the intensity needed to get the better of the top guns in world tennis.