TWO years ago, when he won the French Open to complete a career Grand Slam, Roger Federer was rightly being lauded as arguably the greatest tennis player of all time.

Twelve months later, he was being eclipsed by another all-time great, Rafael Nadal, who claimed the Wimbledon and US Open titles in 2010 to establish his own exalted position in the annals of the game.

So if Federer was the best, and Nadal was the man who became better than the best, what on earth does that make Novak Djokovic as he approaches the end of a season that has seen him achieve feats that few thought possible?

If Djokovic had done what he has done this year at any point in tennis history, he would be hailed as a worthy rival to the likes of Fred Perry, Bjorn Borg and John McEnroe. Add in the fact that he has repeatedly beaten two of the greatest players ever to hold a racquet in order to claim three of the four Grand Slams and a position at the head of the world rankings and you begin to appreciate the enormity of the Serb's achievements.

The statistics are staggering. Of his 66 matches since the start of 2011, Djokovic has won 64. His only defeats came at the hands of Federer, in an epic French Open semi-final, and Andy Murray, when injury and fatigue finally caught up with him in the final of the Western & Southern Open.

As well as his three Grand Slams, he has claimed eight other titles, beating the previously impregnable Nadal on all six occasions they have met in a final. Despite his two defeats, his dominance over both Federer and Murray is equally emphatic.

The extent of his improvement in the space of a year is staggering. He always had ability, but it is not too long ago that he was being posited alongside Murray as ‘the best of the rest' behind Federer and Nadal. Now, for all of Murray's achievements on the ATP tour, the pair inhabit a different plain when it comes to a major championship.

So what has Djokovic done to become such an effective manifestation of the complete player? There have been numerous minor improvements that have contributed to this season's success, but perhaps the most significant is the physical transformation that has occurred over the last few years.

At the start of his career, the 24-year-old had a reputation for being physically weak. He was dogged by a succession of niggling injuries, his stamina would sap in the latter stages of matches, his chances of surviving a five-set examination in the latter stages of a Grand Slam were negligible.

Compare that to now. He might not boast the bulging biceps of a Nadal, but Djokovic's physical strength is considerable. No one covers more ground in the course of a game, no one, not even Nadal, retrieves more lost causes, and no one keeps pounding away from the baseline with the same level of consistency and force.

Knowing that his body will not break down on him, Djokovic relishes the kind of five-set battle that enabled him to overcome Federer in last week's semi-final at Flushing Meadows.

With his physical frailties banished, the mental side of his game can come to the fore. While Murray's character tends to give way when the pressure is most intense, Djokovic appears to revel in the heat of battle.

He is a fighter, upbeat and expressive when things are going his way, steely and determined when he needs to dig deep to transform a match. He is also exceptionally driven, a trait that has enabled him to maintain his exceptionally strong form this season no matter what the surface, profile of tournament or strength of opposition.

When he won in Montreal earlier this year, he became the first player since Pete Sampras to win his next tournament after becoming world number one. In Djokovic's eyes, this is the beginning rather than the end.

His game does not have a significant weakness, and the reliability of his shot making means it is hard to see any particular surface causing him problems. Once in a blue moon, he might lose to either Federer or Nadal, but the defeats will be anomalies, exceptions that prove the rule.

He will end 2011 as the foremost performer in any sport. While tennis, like all pursuits, stands still for no one, it is hard to see 2012 being any different.

-

SO where does that leave Murray? As the fourth best player in the world is the answer, hardly an achievement to be sniffed at, but hardly the moniker he dreamed of at the start of the season.

The elusive maiden Grand Slam remains as far away as ever, with the British number one having reached four semi-finals in the last 12 months, three of which he lost to Nadal. When he did make a final, at the Australian Open in January, he was outclassed by Djokovic and fell into a slump that lasted for the best part of three months.

He could get lucky. Injuries could fall for him, as they have for other players in the past. But unless there is a series of shocks in the early rounds, he will always have to beat two of Djokovic, Federer and Nadal to win a Grand Slam. And at the moment, that looks an all but impossible task.

-

SPEAKING of impossible tasks, Jonny Wilkinson could have done anything on Saturday morning and the ball still wouldn't have gone between the posts as England edged out Argentina in their opening World Cup fixture.

Perhaps it was just a bad day at the office. But Wilkinson hasn't had too many of those in the past and was clearly still tortured by his failings as he eschewed the opportunity of a day off on Monday to cram in some extra practice.

Wilkinson's reliability has been the key to World Cup success before, but if he isn't kicking penalties, the former Newcastle Falcons fly-half doesn't bring too much else to the party. Give Toby Flood a go against Georgia on Sunday and see if that brings some tempo and urgency to England's game.