Chris McGrath: Balding, tubby and on the bench. But he can still set Mexican hearts racing

Every manager at the World Cup hopes that he has players capable of making a decisive impact from the bench. Javier Aguirre is perhaps the only coach able to summon someone who can also make a similar impact on the bench itself – unless, that is, it has been assembled from particularly robust materials.

The ideal substitute comes skimming over the turf, terrifying tired defenders with his energy and agility. But Cuauhtemoc Blanco will be unleashed during Mexico's crucial game with France today as though he has jumped out of a hot air balloon, wearing a telephone kiosk. Blanco makes Tomas Brolin look like Gisele Bundchen.

Frowning and balding, Blanco gives you a sense of how James Gandolfini, the man who gave us Tony Soprano, would play a failed darts player. He is 37 now, the oldest outfield player at the tournament, and barely looks in shape to keep up with a Sunday morning pub team.

But there is far more to Blanco than meets the eye, which is saying a good deal. Though he can only be deployed sparingly, nowadays, he is probably the most incongruously ethereal talent at this carnival. When he waddled on to the pitch at Wembley last month, he immediately showed how he can still flummox younger opponents with his sleight of foot, and spry football brain. In Mexico's subsequent friendly against Italy, he jogged on for the final 20 minutes and released Alberto Medina with a delectable chip to seal victory.

And it was the same last Friday when Blanco began his third World Cup, against the hosts in the opening fixture, as one of the great folk heroes in Mexican football history. He entered after 68 minutes, and soon restored a centre of gravity to a team that had dominated the first half but now looked dispirited after falling behind. They equalised within 10 minutes, and at the end Blanco was mere inches too high in setting up fellow substitute, Javier Hernandez.

Blanco only returned to national service last year, as Aguirre began to salvage Sven Goran Erikkson's qualifying shipwreck. He had been omitted from the 2006 squad by Ricardo Lavolpe, prompting furious protests outside the national FA. One placard, depicting the crucified Blanco, read: "Forgive them. They know not what they do."

Now his very presence in the camp is intended to fortify some high-calibre young guns in the Mexican attack. Giovani Dos Santos and Carlos Vela are both only 21, but Blanco's irresistible foil is Hernandez, 22, whose recruitment by Manchester United seals his status as the emerging idol.

It is Hernandez who is transforming Blanco from playmaker to kingmaker, as much a mentor off the pitch as the ignition on it. Yet they could scarcely be more different, and apparently angry words were exchanged after Friday's game. The Mexican press has since reported, with palpable relief, that the two have been spotted chatting amiably during training.

Blanco emerged from Tepito, the notorious barrio bravo of Mexico City, where every alley throbbed with danger; Hernandez, a son of the nation's footballing aristocracy, was raised in rural affluence. His grandfather and father both played in World Cups, Javier Sr in 1986, when they reached the last eight. He has been reading business studies at an elite university, living with his parents, and remains reticent in demeanour and expression; Blanco is volatile and vivid.

It is said that Blanco plays up to the hot-tempered image and that he does charity work in secret because he deplores the shallow attention. Regardless, he is a true popular champion, not least for a Hispanic underclass north of the border, which cherishes any boy from the barrio who makes good. When he arrived at Chicago Fire in 2007 – at $2.7m a season, the most remunerated MLS signing after David Beckham – 6,000 turned up for the news conference.

Blanco bears the name of the last Aztec emperor, Cuauhtemoc, who was tortured and hanged by Cortes. It is, perhaps, too much to hope that he can deny the Spanish a first World Cup, but he can certainly gild his own, anarchic dominion with a final, unfeasible flourish or two. Perhaps he will even wheel out the Cuauhteminha – the comical bunny-hop he patented in his first World Cup, 12 years ago, jumping out of a tackle with the ball between his ankles. A quarter-final defeat of the US might not exactly have the world at his feet. Back home, however, it would confirm Blanco as worth his weight in gold.