James Lawton: How can one man represent so cleanly and unwaveringly a football dream and the other so relentlessly occupy a nightmare?
It is not the story of two amigos so much as compatriots who came to play their football this week not in different countries but separate planets. The trajectory of one of them remains astonishing -- or in the more lyrical words of the Spanish press, 'infinite and eternal.'
That's what a record 234 goals, a fusillade of 17 in the last seven matches and an eighth hat-trick of the season for the team generally agreed to be the finest on earth does for the already mystical reputation of Lionel Messi.
Meanwhile, his fellow Argentinian Carlos Tevez gave just one glimmer of the drive and the cutting edge that made him an emerging star while the teenaged Messi fretted on the bench during the 2006 World Cup.
But if the comparison had most to do with the mysteries of human nature and genius -- and the inescapable conclusion that one man is increasingly touched by the football gods and the other will forever be beset by its demons -- Tevez still did something extraordinary.
In one moment of superior instinct and skill, he helped put Manchester City back on course for a most serious challenge for their first title since 1968. What we had was the workings of a natural-born footballer, a flash of the purest intuition when he played a killing reverse pass into the path of his match-winning team-mate Samir Nasri.
And inevitably the questions poured in once more. The most pervasive of them asked how it is that one man represents so cleanly and unwaveringly a football dream and the other so relentlessly occupies a nightmare.
If nature and background are doubtless two keys, there is plainly the impact of their hugely different career profiles.
While Messi has grown up under the patronage and fine attention of a club whose methods have become not so much a model as an ideal, Tevez became the property, along with Javier Mascherano, of football entrepreneur Kia Joorabchian.
Barca gave the diminutive Messi a series of arms around his shoulders -- and growth hormones.
Tevez, it is hard not to believe, was more than anything in receipt of a sustained lesson in the profit motive -- at Boca Juniors, Corinthians, West Ham, Manchester United and City.
In the course of the legal actions, the controversies and an ultimate sense of moveable loyalties, Tevez has become a prime example of what can happen to even the most gifted individual in today's football culture.
Certainly the events at the Etihad Stadium this week touched the surreal.
City's manager Roberto Mancini, who declared that Tevez would never again play for him after his refusal to come off the bench in the Champions League game in Munich last year, was reluctant to dwell on the degree of compromise represented by his decision to send him into the pivotal stage of the crucial victory over Chelsea.
"He has apologised -- and his apology has been accepted," said Mancini and then, after Tevez's life-giving intervention, "he has made a fantastic contribution to this important win. I'm very pleased and, remember, he is not yet properly fit."
At this point, plainly, Tevez has become less a moral conundrum than potentially a vital means to an end.
There was a ripple of boos when he went on to the field but they were drowned soon enough by the reality that he did indeed retain the ability to inject something dynamic into a fading title challenge. If he had defected quite shamelessly, if back in Argentina he had sneered at the city which had embraced him so warmly, here he was back in the colours, back at the heart of their yearning to be the best team in England.
At 28, Tevez had become the ultimate football mercenary -- a property who has, apparently, two vital services to perform for the club who have sought to buy their way to glory.
Despite all his baggage, he can help in the first vital stage of the project and in the process he can beef up his personal value that was rated too low when Internazionale and Milan came calling to end his exile in Argentina.
For City and an ostensibly contrite rebel, pragmatism now reigns.
For Barcelona and Messi an extraordinary story spills into the sun-lit realm of fantasy.
The details of his challenge, at the age of 24, for a unique place in the annals of the game to which he brings an apparently endless invention moved up another notch with his hat-trick against Granada. On strike rate he is now required to bend the knee only to Germany's legendary Gerd Muller, Der Bomber, who for Bayern Munich scored 398 goals at 0.88 per game, and Milan's Gunnar Nordahl, whose 221 came at 0.82. Muller performed for 15 years at Bayern, Nordahl 17 for Milan.
Messi, on a rate of 0.75 over 314 games, already dwarfs the Spanish demi-god Raul (0.44) and Thierry Henry (0.61) as he stands as not only a supreme virtuoso but a man of unshakeable balance and maturity.
What is left for him to achieve, how can he further shape the debate that puts him into contention with the greatest players of all time, his compatriots Diego Maradona and Alfredo di Stefano, the eternal Pele, and Johan Cruyff?
Some say he needs to win a World Cup, as Maradona did just about single-handedly in Mexico in 1986, or Pele so imperiously in 1970, 12 years after his eruption as a teenager in the 1958 tournament. Others say the old yardstick has become irrelevant, that as the importance of the World Cup dwindles Messi now operates in the great arena of the Champions League, where the most expensive talent and highest ambition is most ferociously concentrated.
It left us with one certainty this week. It was the chasm separating the two distant amigos, the ones occupying the different planets -- and understanding of their places in the world's most compelling game.
Messi reminded us that he was sublime. But then, when you thought about it, Tevez also did something remarkable. In one flash of the best of himself, he said that against all the odds and available evidence, he might just be worth the trouble, give or take a principle or two.