Ten-time Grand Slam winner Rafael Nadal is in a slump. 2011 has not been the kindest year for him, and his record has weakened somewhat for it.

Nadal has proven to be human after all. He has won just the three tournaments (unsurprisingly, all on clay) and none since June. He's lost both his air of invincibility and his number one ranking. Nothing quite illustrates his fall off the top of the tennis world like his 2011 record against Novak Djokovic. It reads like a tennis nightmare: 0-6.

He did win the French Open, but in other news, Australia has a female Prime Minister.

Roger Federer beat Nadal last night, leaving him one loss away from crashing out of the ATP World Tour Finals. It wasn't just the result that is cause for concern, though, but the manner of the 6-3 6-0 defeat. He hit just four winners to Federer's 28. Federer broke him to love in the opening set. Nadal won just nine points in the second.

A little over a month ago, Nadal tumbled out of the Shanghai Masters in the third round, losing to Florian Mayer in straight sets. Two weeks before that, he was clobbered by Andy Murray in Tokyo. Nadal took the first set in that match, but lost 12 of the next 14 games. He was again kept to a donut in the third set.

In August, he was ousted from the Rogers Cup in Canada in the second round by Ivan Dodig. Four months before that, he had dispatched the unheralded Croat 6-3 6-2.

How does the all-powerful, all-conquering Nadal come to put in performances like these? What's gone wrong?

The first thing to note is that it is very hard to maintain the sort of dominance that he has achieved. While you're winning, the world it rosy and your opponents shudder when they hear your name. But lose - even come close to losing - once, and all of sudden you are beatable. Belief returns and the all important "air of invincibility" disappears.

A marked downside of being on top is that your every move gets studied. All your opponents begin to formulate strategies to beat you in particular. Just ask Collingwood.

However, while others rise to the occasion when they play him, his own game has definitely dropped. His flat, scorching backhand has eluded him of late, or perhaps he hasn't been confident enough to maintain it. His average serve speed has dropped markedly, by almost 25km/h. Indeed, he conceded after the Federer loss last night that he needs to get back to winning more "free points" off his serve.

Admittedly, he has battled injury during the year, but I doubt even he would accept that as an excuse. The biggest source of the problem probably lies between his ears. It can't be easy to watch as your grip on top spot slips away, seemingly unable to do anything about it. It takes an incredibly strong character to stay positive while that's happening.

Of course, for any other player, a year of 66 wins for 13 losses at a winning rate of 83%, with a Grand Slam title and two Grand Slam finals, would be cause for celebration. That this year is a decline on previous years only speaks for his overall greatness.

And just as Federer seemed unbeatable until Nadal arrived, and Djokovic proved to be the Spaniard's kryptonite this year, the Joker will not be able to maintain his present wave of brilliance. He will be brought back to the pack in due course. Perhaps Andy Murray or Jo Wilfried Tsonga will have their turn soon.

That is, if Rafa doesn't beat them to it. He's only 25. There's a lot of breathtaking tennis still to come from that magical left hand.