Michael Visontay lectures in Sport, Media and Culture at the University of NSW.

The problem with Roger Federer is that we love him so much we can't think straight about him anymore. When the Swiss maestro completed a career slam two years ago, a global wave of sentiment poured forth, acclaiming him as the greatest male tennis player of all time.

Of course it was premature but Federer's magnetism was almost irresistible - to everyone but Rafael Nadal, who achieved the same feat at just 24. Now the Spaniard stands on the threshold of winning a calendar slam, the first since Rod Laver in 1969.

That makes this year, 2011, the true moment of judgement. The upcoming Australian Open will usher in a watershed season for both players. For Nadal, there looms a place in history beyond debate, and a reign of authority that may last for years. For Federer, there is the opportunity to achieve something even greater: roll back the Nadal juggernaut and reclaim his mantle.

Rarely has debate about tag of "greatest" been so muddied as it has been with Roger Federer. He has won more grand slams than anyone else. During the golden period of 2004-07, he won an incredible 11 out of 16 grand slams, and was finalist in three others. More significantly, he plays a brand of tennis so complete, so aesthetically beautiful that men, not just women, swoon at him on the court. Federer has raised the artistry of tennis to a level never seen before.

Yet for all those achievements, he has, bizarrely, lacked the total dominance we - and he - would have expected. The capacity of teenage Nadal to humiliate him annually in Paris, rise up on the sacred Wimbledon grass, and then repeat the dose in Melbourne and New York, has thrown a spanner in the pantheon.

For a player with Federer's sense of history, it's hard to stomach. Nadal's ascendancy has eroded his self-belief: the Swiss player's dreadful conversion of break points against him ranks alongside Greg Norman's fourth round collapse as one of sport's greatest chokes.

Against any other player, Federer can look into his record and find a memory of victory. Against Nadal, when he looks back, he sees failure rather than success, doubt instead of confidence, notwithstanding his season-ending victory at the Masters in London.

So for Federer, the Australian Open will be much more than a matter of merely thwarting Nadal's grand slam dream. Federer is 29, with 16 grand slams to his name. The man whose record he beat, Pete Sampras, won all but one of his 14 slams by that age. And Sampras did not have a Nadal as his rival. He had Andre Agassi, a great rival, but not in the same league as Nadal for skill, intensity, or achievement.

In short, Federer will have to find something unprecedented to regain the ascendancy and through that, a renewed claim to being "the greatest".

Nadal, on the other hand, stands poised to eclipse Federer's career record. If the Spaniard wins in Melbourne, he will be compared to Rod Laver, with some justification. The Rocket won his first grand slam at the same age, 24, but that was as an amateur, against thinner competition than Nadal faces. The depth of the men's tour and the quality of the top 10 players, in particular, is well beyond that which Laver had to face.

In the longer term, Nadal has now created a path, if his knees hold out, to establish a dominance over his rivals, and across all surfaces, that may make him the player who ultimately will be judged as the greatest of his time - greater even than Federer - and invite permanent comparisons with Laver.

We are on a cusp. As the public wills Federer back up to the pedestal he occupied so elegantly, Nadal is moving inexorably to a higher peak. Federer's tennis is divine, but Nadal may yet prove to be closer to god.