“Three months ago some people wanted to strangle him,” Massimiliano Allegri said with a smile, but that night they just wanted to hug him. The story goes that when Dani Alves arrived at Juventus, Gigi Buffon took him to one side and asked him to teach them how to win the Champions League. He might not be able to do that exactly but Allegri was speaking just after Alves had taken them to Cardiff, delivering the pass for the first goal and volleying home the second in Monaco. He had already provided two assists in the first leg of the semi-final in Turin, one with a superb backheel. Juventus were in the final again, two years after they lost to Barcelona in Berlin– when Alves was on the other team.

On the other side this time, facing him, will be Marcelo, who after Real Madrid’s recent clásico defeat bemoaned: “It’s my fault.” His crime: not committing the foul that might have prevented Lionel Messi from winning it. Few noticed then that he had provided the late assist for James Rodríguez to equalise in the first place – but they did when six days later he scored late to tighten Madrid’s grip on the title. Five days before that, he had finally broken Bayern Munich, in the 109th minute of the Champions League quarter-final, weaving through, hurdling challenges and leaving Ronaldo an open goal to finish off the German champions.

And so here they are, meeting again, this time in Cardiff on Saturday. International team-mates and for so long opponents in club football’s biggest rivalry: two “defenders” who are so much more than that. Full-backs? Footballers, full stop. Brilliant, too. Brazilians, both. Different, breaking the mould. “I don’t want to be just another player,” Alves says, and he is not. Nor is Marcelo. Automatons? No, thanks. Better to embrace the game, enjoy it – and, lest it be forgotten, win it too. Between them they have 53 trophies in total, soon to be 54. They are key men, arguably even the key men, in the best two teams in Europe.

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Over the years it has not been hard to find their critics, but seek them among their own and it is a different matter; even some will admit these are men who can take a bit of getting used to. They cannot defend, detractors say, but that line is as facile as it is flawed. It also feels as if it goes beyond football: if you dare to smile, as they do, the accusation deepens, as if the sport has to be a deadly serious business, as if enjoying it means you are not committed, when they clearly are.

Every squad needs personalities – “contagious” is the word Zinedine Zidane uses to describe Marcelo – and fun does not equal frivolous; you do not play for eight years at Barcelona and a decade at Madrid without dedication. Juventus do not sign you and Barcelona do not decline without you; if they thought they would not miss Alves, they were wrong. “People automatically think that because you attack, you can’t defend. Not true,” Alves said. That was five years ago but it could have been yesterday. He has not changed; it is others who have, some recognising his contribution late, a process that finds parallels with Marcelo, now more than ever.

It should not have taken so long. It is not just that it is false that they cannot defend; it is, Alves says, that the terms need tying down. “What,” he asks, “is ‘defend’? That no one ever dribbles or attacks? Bloody hell, football would be boring, wouldn’t it? You can prepare [only] to defend but then the guy dribbles past you anyway ... what, you think you’re the only one that’s quick? If you ‘defend’, you don’t attack; if you ‘attack’, you don’t defend? What’s football for? To win. And to win you have to score more. The winner isn’t [just] the team that defends incredibly; if you defend well but don’t score, it’s worthless.”

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Even in Brazil, they have not always rushed to embrace the pair. There may have been occasional doubts – Marcelo did not start the 2014 final against Atlético Madrid in Lisbon and Alves’s relationship with the Barcelona board was always fraught – but what they offer far outweighs any flaws. If they attack, it is because their managers want them to, because they are good at it. They are following orders, not breaking them. They have played well over 1,000 games between them, at the most demanding clubs on earth.

Marcelo started playing what Brazilians call futsal and Spaniards fútbol sala – indoor five-a-side – at the age of four. His brother-in-law plays professionally and in his first couple of years at Madrid Marcelo would often escape to play too, even joining competitions. In an interview with a futsal magazine, among the few he has given, he admitted he would like to see out his career on the court rather than the pitch, back where it began. Marcelo’s brother-in-law highlights his “dribbling and technical skill, the ability to improvise to get out of difficult situations when no one thinks he can”.

In part, that is inheritance rather than coincidence: Marcelo and Alves are products of their environment and experience. Futsal is played with a smaller, heavier ball that flies round the court, almost always on the floor; a game of touch, speed, technique and thought. “I had the pleasure of playing futsal at school,” Alves said. “And what it gives you is intelligence: it’s a sport where you need to use your head. There’s very little space, the marking is very tight, so you need to be smart, very quick thinking. In football people who have that intelligence have a big advantage over others.”

It is not just that they are “defenders” who attack; it is that they are defenders who play; it is the way they attack. Full-backs bombing up the line are one thing, Alves and Marcelo are something else: they come inside, take responsibility, create, seek one-twos, take people on – and not just with the drop of a shoulder and a burst of speed, as if they were No10s, only in the wrong position. “Full-back” is just a clue and sometimes it is a red herring.

This season Marcelo has been arguably Madrid’s best player. At Sevilla everything went through Alves. At Barcelona he provided more assists than anyone in Spain, after Messi. At Juventus, he has created more chances than anyone in the Champions League. “Did you see him?” asked a beaming Allegri after he performed so superbly against Monaco. “Did you see his assists? That’s what a central playmaker does.”

It is similar to what Marcelo does too. Jorge Valdano says: “He brings the ball out with outstanding naturalness and ease; he goes through the middle of the pitch as if it was his own home and, when he gets to the top of the pitch, he has the solutions a forward has. We’re used to full-backs like Gordillo or Roberto Carlos who plough the wing; Marcelo goes by planting flowers.”

As for Alves, Giorgio Chiellini admitted he was “crazy for our culture” and that assimilating him was “hard at first”, but he was “like Messi”, on “another level technically”. So here they are, Brazilians of similar spirit, players who love to play. In purple is Marcelo, seeking his third European Cup in four years; in black and white Dani Alves chasing his third treble in eight seasons, and his 34th major title. It is not bad for two defenders who cannot defend. Who wins no one knows yet but it should be fun finding out.