There is a moment towards the end of the recent BBC documentary Whistle to Whistle in which, after an hour of fixating on the details and minutiae of his job as Belgium coach, Roberto Martínez finally allows himself to take a broader view. “I just feel that this generation deserves silverware,” he says. “They deserve something that will be talked about for the next 50, 60, 70 years. But that doesn’t mean it’s going to happen.”

In those few sentences, Martínez expresses the fundamental paradox of his job, in many ways the fundamental paradox of international football. Since taking over from France in October 2018, Belgium have now been top of the Fifa world rankings for almost three years. They have, by most statistical and qualitative measures, been the world’s best team. The problem, when you get to the sharp end of an international tournament, is that you only get 90 minutes to prove it.

It is a problem that been occupying Martínez’s days and nights ever since he took the job in 2016: how to convert that weight of talent, that mountain of expectation and longing, into one result on one evening. This is the ornate violence of knockout football: that stark contrast between the dozens of games that don’t really matter, and the handful that mean absolutely everything, upon which legacies and careers rise and fall.

On Sunday afternoon Belgium will face Portugal in Seville as strong favourites to progress to the last eight. They cruised through their group with three wins. All the noises from the camp suggest a harmonious, confident team slowly building, slowly sharpening to a point. The attacking trident of Romelu Lukaku, Kevin De Bruyne and Eden Hazard is just coming to the boil. This all matters. You could also make a case that none of it matters.

Prominently displayed in Martínez’s office in Tubize, just south of Brussels, is a graphic print representing Nacer Chadli’s winning goal against Japan at the last World Cup. Belgium won 3-2 after trailing 2-0 in the 69th minute, and for all that came before and after, there is a strong case for anointing Chadli’s 94th-minute goal as the most important in the recent history of Belgian football. Had Belgium gone out in the last 16, the tale of their tournament – and perhaps this generation – would again have been one of lavish underperformance. The tag of tournament chokers would have been almost indelible. The clamour for purgation and revolution – starting with Martínez himself – would have been irresistible.

Nacer Chadli is surrounded by teammates after his winner for Belgium against Japan in the 2018 World Cup last 16
Nacer Chadli is surrounded by teammates after his winner for Belgium against Japan in the 2018 World Cup last 16. Roberto Martínez has a graphic print of the goal in his office. Photograph: Francis R Malasig/EPA

And so Belgium’s trilogy of knockout performances in Russia serves as a salutary lesson in the fine margins at this rarefied level. After the escape against Japan, Martínez decided on a wholesale tactical shift in the quarter-final against Brazil, converting an attacking 3-4-3 into a counterattacking 4-3-3: a change enacted with just 20 minutes of training in advance. “What’s he doing?” Hazard remembers the baffled players asking each other before the game. But it worked: Belgium comprehensively peeling Brazil open on their way to a 2-1 win.

The semi-final against France was different again. Belgium dominated possession and territory, only to lose to an inspired defensive rearguard and a single set-piece goal. Yet amid the anger and injustice – “We lost against a team that was not better than us, and which did not play,” said Thibaut Courtois – there was also a measure of self-culpability in the way one of the world’s finest attacking teams had ended up swinging crosses on to the head of Marouane Fellaini.

This, then, is the moment when we discover whether Belgium have learned how to navigate the unique currents of tournament football: a task that requires a little luck and an ability to roll with the punches, to manage games with intelligence, to find the little moment of coolness and class that unlocks elite defences.

Portugal are not the team they were five years ago: they feel passive and flat-footed at the back, too vulnerable to pace, too reliant on the goals of Cristiano Ronaldo. Increasingly this is beginning to look like a tournament too far for Pepe. Belgium should win if they concentrate on their own strengths. But in that “should” is buried a multitude of curses as well as blessings.

Romelu Lukaku watches Hugo Lloris save a shot from Toby Alderweireld as Belgium came up just short in the 2018 World Cup semi-final against France
Romelu Lukaku watches Hugo Lloris save a shot from Toby Alderweireld as Belgium came up just short in the 2018 World Cup semi-final against France. Photograph: Martin Meissner/AP

The other factor here is time. This is the second-oldest squad at Euro 2020, after that of Sweden. Ten of the Belgians are over 30; all but Tielemans and the promising striker Jérémy Doku are over 25. The first golden generation – Vincent Kompany, Fellaini, Mousa Dembélé, Toby Alderweireld, Dries Mertens, Jan Vertonghen – have already either departed the scene or are on their way out. Meanwhile, the under-21s didn’t even qualify for this summer’s European Championship, while the under-19s are officially ranked the 16th best in Europe.

There is still plenty of talent there – Doku, Milan’s Alexis Saelemaekers, the Stuttgart midfielder Orel Mangala – and a fine infrastructure in place to nurture it, much of which put in place by Martínez in his dual role as technical director. But given Belgium’s size, and the improbability of unearthing another generation remotely like this one, you still feel Belgium’s time is either now or not at all.

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And so, for all their years of peerless excellence, the legacy of Belgium’s greatest generation really boils down to these next four games. Of Belgium’s last 58 opponents, only two have managed to prevent them from scoring. One was France in the World Cup. The other, in a goalless draw in Brussels in June 2018, was Portugal.