In the end, no one could catch Barcelona, not even the Espanyol fans who chased them off the pitch and down the tunnel – although they got closer than anybody else. The banner at the RCDE Stadium on Sunday had declared “we are Espanyol and this is our life”, yet it wasn’t one they chose, still less one they liked. They had never seen their team win a derby in the place they made home, and this time not only did they witness another defeat that pushed them ever closer to a second relegation in three seasons, but the few who hadn’t left early also watched their rivals celebrate becoming champions in their own back garden. For some – morons, mostly – it was too much to take.

Out there in the centre circle Barcelona were dancing a sardana, a ring of players and staff spinning, when suddenly they broke into a sprint instead. There had been no provocation and they hadn’t even been there three minutes, the coach Xavi Hernández already deciding it was enough, that this was neither the time nor the place and calling them to come in, when it happened. In the south stand, some Espanyol fans – a couple of hundred perhaps, many with faces covered – smashed barriers, climbed on to the pitch and began a stampede, heading for the players. Alerted just in time, Barça set off straight for the sideline, bundling in. Some fell as they went, others were caught up in it all, scared. As he ducked beyond the forming cordon, Frank Kessié smiled.

Related: Barcelona seal La Liga title but invoke Espanyol fans’ wrath

There, from behind police and security staff hurriedly trying – and not always succeeding – to block off the entrance to the tunnel, they watched missiles being thrown, chairs and bottles flying, and listened to the abuse. Some supporters turned to look up at the directors’ box and demanded resignations. One kicked over a TV camera; he, it turned out, was on the list for the Partido Popular at the municipal elections and is a kids’ coach. Inside, there were confrontations, players pushed back: Ronald Araújo and Sergio Busquets especially. “It’s a pity, but it’s football, it’s life,” Barcelona’s captain said. “What matters now is to celebrate, to be happy.”

In the dressing room, they did and they were. The club president, Joan Laporta, barrelled in: rolling and bouncing about, suit soaked, tie tugged to one side, dirty kit thrown at him. Araújo, hair dyed blue and red – “I reckon I look nice like this” – was streaming on Instagram and Lionel Messi had joined the chat. Seven kilometres away, back towards the city, a crowd was building at Barcelona’s Joan Gamper training ground, first stop for the players who piled on to the balcony above. More supporters gathered around the Canaletes fountain, a traditional meeting point at the top of the Ramblas. What time’s the curfew, Xavi was asked. “Nah, tonight there’s freedom,” he said. “This deserves a big celebration.” On Monday evening, they will take a bus through the city alongside their all-conquering women’s team.

Back in August 2019, Messi expressed his hope that one day people would realise how hard it is to win the league. Barcelona had won their eighth in 11 years four months before that, but there had been no bus. Anfield was coming up and the domestic title was, well, assumed. The night they clinched it, the players wore T-shirts saying, “the extraordinary thing is that it seems normal”. This time was different. They had seen, been reminded, how hard it can be to win a league, learned to love it. This was extraordinary, full stop, and no longer normal; this is the first time Barcelona have won the title since then.

Four years is not exactly an eternity, but it can feel like it. Especially when enough has happened for a decade anywhere else. And if this is the kind of “crisis” many clubs would crave, it is also real and this felt cathartic. The T-shirts they wore this time said: “The league is ours, the future too”. Over-optimistic, perhaps, but maybe there’s something in that, however small, and it spoke of an emotional need. “We’ve brought the happiness back,” Laporta said.

This is Barcelona’s first league title without Messi this century. Halfway through the season, Gerard Piqué announced his retirement– he has been invited to join the celebrations – and Sergio Busquets will not continue, his ninth title to be his last. “I wanted to leave with this,” he said. Only four other squad members – Marc-André ter Stegen, Jordi Alba, Sergi Roberto, and Ousmane Dembélé – have won the league here. “This is important for the generation that’s coming,” Araújo said; “It’s the first for many of us,” Raphinha said.

“If I had asked the journalists at the start of the season if we would win the league, and with an advantage like this, few would have said yes,” the Brazilian added.

Real Madrid have failed to win three league games in a row since the World Cup and Atlético fell early, but it is not just about their failure to compete. If Barcelona’s double European capitulation and the 4-0 defeat to Madrid in the Copa del Rey semi-final inevitably invite questions, domestically their success is as incontestable as it is unexpected. Barcelona are 14 points clear with four games to spare. They have 85 points already, one point off the title-winning totals of Madrid and Atléti from the last two years, and could yet reach 97, the third-highest total ever. Barça have been top since October. Ultimately, nobody got near them. And yet if that makes it sound easy, like they have rolled over everyone, it has not been that either.

This is a different Barcelona, a different era. It is still, Xavi insists, a team under construction but it is a side, he said, whose success has brought stability. Although that is not a point he drove home, it is an important one. This is a team that have won the league at a time of change and financial crisis, working within a club with €1bn debt, building work at the Camp Nou about to force them into exile at Montjuïc, and with the Negreira case as a backdrop, all the noise that has surrounded them.

This is a club that needed to pull on the infamous palancas to build this squad in the first place – a risk some will consider vindicated now, at least short term – and still has a salary mass €250m too great, where new contracts for Gavi, Araújo, Marcos Alonso and Sergi Roberto can’t yet be formally registered. A club that Mateu Alemany, the director of football and architect of it all, is leaving at the end of June.

All of which might be part of the reason why Barcelona have won it with their fans, noisily packing the Camp Nou with average crowds of at 84,000 – it is as if those problems, this new era, has made them more aware than ever they have a role to play, support to offer. It certainly has made them aware of the shortcomings and willing to seek solutions, new ones.

When they lost the way they did at the Bernabéu in October, winning the league seemed implausible but they have competed like no one, including themselves. This may be the least Barcelona of all Barcelona teams, which makes winning the title feel even better – or at least more meritorious, overcoming obstacles that might have once been insurmountable.

The clásico brought a shift, a “tactical variation” according to Busquets. Gavi played supposedly in the front three but was more part of a four-man box in the middle. “No one knows what to call his position,” Ter Stegen admitted, but whatever it was it worked. “We had brilliant games and others where we had to roll up our sleeves,” Busquets said. The words he used to describe Barcelona were: “solid”, “stable” and “solidario”, adding: “The defensive numbers were good.”

Very, very good. With 21 goals scored, this has been Robert Lewandowski’s league, especially early in the season when AS described him as “a water diviner, some sort of mystic [who] had found an oasis in the desert”. It might have been Pedri’s too, and in terms of points and play he has been vital, although he has only started 22 of the 34 games. Dembélé started well – very much Xavi’s success, against the wishes of a club that wanted him gone – but then got injured, which is where Raphinha took over.

But it was also Gavi’s league, as much for his feistiness as his football. And Busquets’s league, at 35. And Frenkie de Jong’s, after they had tried to force him out. It belonged to Alejandro Balde, a revelation; to Andreas Christensen, silently superb; and very definitely to Araújo, the man who had Xavi applauding a big hoof into the stands. When it came to the vital moment, it was Kessié’s league too, the president’s clásico goal in March all but ending the title race.It was certainly Ter Stegen’s league too, possibly more than anyone else. He was the one man unhappy at how Sunday night went, two insignificant goals irritating him: they were after all, a sixth of all those he has conceded all season, a symbol of the shift. At 88%, no one in Europe has saved more shots. On 25, no one has kept more clean sheets; one more and it will be an all-time record. He has let in 13, thirteen, in the league, on course for another record. Only two have been at the Camp Nou and they were a penalty and an own goal. On Sunday Barcelona scored four; on many nights it has been just one. A third of their games have finished 1-0.

“This is an extraordinary league, brutal, and we have to really value the way we did it: at times, we played very well, at others we showed we know how to suffer, how to be a block,” the coach said.

That may not sound much like Xavi, the ultimate ideologue, defender of a footballing faith, but he has shown the intelligence and adaptability needed and together they have found a way. If there has been debate about their identity even while they won – proof, he says, that this is the hardest place there is – there can be none about the achievement. Despite being welcomed home as a hero, still few truly expected this. He took over at a time of crisis and changed the culture, an evolution begun and although he had won eight league titles as a player, this is his first as manager, loaded with a responsibility that goes beyond just the team and makes it different.

Mallorca 1-0 Cádiz, Real Sociedad 2-2 Girona, Osasuna 3-1 Almería, Villarreal 5-1 Athletic, Real Madrid 1-0 Getafe, Celta Vigo 1-2 Valencia, Elche 1-0 Atlético Madrid, Valladolid 0-3 Sevilla, Espanyol 2-4 Barcelona.

Monday: Real Betis v Rayo Vallecano

So, he was asked, once the champions had escaped the stampede and were safely inside where the celebrations could begin properly, the title theirs four years on, is this Xavi’s league?

“No,” he said, “it’s Barcelona’s.”