Implausible as it might seem, Roger Federer and Rafael Nadal share precisely the same height and weight: 6ft 1in, and a rigorously controlled 188lb. It is some freak of genetic divergence that two such antithetical specimens could ever be sculpted from the same raw material and yet their rivalry, which reaches its 33rd and perhaps final defining instalment in Melbourne on Friday morning, has always been derived less from their common ground than their plenitude of exotic differences.
Where Federer is more comfortable in the company of Anna Wintour or Credit Suisse suits, for example, Nadal would far rather kick back with his closest amigos over the PlayStation in Manacor. The parallels run no deeper than the Nike ticks on their respective bandanas. The polarities, however, help to define their endlessly engrossing duels: innate gift versus unflinching resolve, Swiss understatement versus Latin flamboyance, groomed metrosexual versus piratical brute.
As Jon Wertheim observed in Strokes of Genius, his account of their 2008 Wimbledon final, this was perhaps the ultimate juxtaposition of artist and conquistador. Or perhaps Nadal was just playfully accentuating the contrast in that sleeveless top. As sport's most exquisite treat, the Federer-Nadal dynamic is a delicacy we could not have dared dream we would still be relishing. Having reached its finest vintage five years ago, its lustre faded just slightly last season as the Spaniard administered fearful thrashings in Indian Wells, Rome and London, heightening the impression that his nemesis was drifting - with supreme elegance, naturally - into the night.
One lone three-set tussle in Cincinnati was not enough to dispel suspicions that the balance of power had swung too far for this to be considered the greatest contest. Federer's restoration in Australia, under the gaze of fellow understated aesthete Stefan Edberg, has shown such conclusions to be spectacularly premature. The only pity, as a consequence of his fall to No6 in the rankings, is that he is not seeded to meet in Nadal in the final. Instead, we must accept that the championship match on Sunday - whether an all-Swiss collision of Federer and Stanislas Wawrinka, or a rerun of Nadal's 2010 Wimbledon triumph at the expense of Tomas Berdych - will have a distinct after-the-Lord-Mayor's-Show flavour next to tomorrow's banquet.
While it is true that Federer and Nadal represent the most gushed-over, lavishly exalted pair in tennis history, they never cease to fascinate as a character study. Where Federer remains a byword for rock-star cool, flicking his hair back with the insouciance of a L'Oreal model, Nadal radiates nervous energy at every step from the rearrangement of his shorts to the geometric alignment of his water bottles. The more romantic members of the tennis parlour have gone so far as to describe this as a clash of artistic styles: Federer the gentle, impressionistic brush-stroker, Nadal the bold and audacious expressionist.
The on-court/off-court dichotomy in their relationship is another compelling draw. Their murderous confrontations in grand slams, where Nadal's cruise to victory at the 2008 French Open was arguably the only match unworthy of them, soften into an almost cloying mutual respect the second they pack their rackets away. Privately, though, their results against each other have moved them to tears. Nadal was a broken man in the wake of his five-set Wimbledon defeat by Federer in 2007, but dissolved not nearly so publicly as his adversary did at the 2009 Australian Open, mumbling through heaving sobs: "Oh, man, it's killing me." This, then, is how powerfully their battles resonate.
Never more so, one senses, than in Chapter 33, as Nadal seeks to reaffirm his supremacy as world No1 with a third slam title in four attempts, while Federer looks to sweep away a few autumn leaves aged 32 with an 18th major and his first since the summer of 2012.
They are united, at least in one sense, by the adrenalin of an improbable resurgence: in Nadal's case, from the ravages of knee surgery, and in Federer's, from misplaced predictions of his imminent demise.
The lines for their reunion in the Melbourne Park crucible could scarcely be more starkly drawn. So if there is scope for a diversion this Friday morning, take a moment to savour. One more time, the odd couple are joined, and again the privilege is all ours.