The lights went out on Camp Nou just before midnight. The lights had gone out on Barcelona a couple of hours before. There weren't many people left; technicians pulling up cables, loading cameras into huge metal cases and wheeling them towards the exit; one last TV presenter resisting, bringing the clásico into Latin American living rooms; and the man they call The Observer. Not for the first time, he didn't like what he'd seen. This had been a bad night for Barça. It was over two hours since Cristiano Ronaldo had dashed towards the edge of the pitch and performed a gesture whose message was clear: "Relax, I'm here." It was over two hours since he had turned up and sorted everything out. Two hours since he brought an end to the match and to the league season. Maybe even to an era.

For Barcelona, hope had lasted two minutes and 19 seconds. That was as long as it took for Alexis Sánchez to score the equaliser, for faith to come flooding back, and for Madrid to rob the ball, string five neat passes together, Mesut Ozil to find Ronaldo, and Ronaldo to go beyond Víctor Valdés to score his 42nd goal of the season. Yes, forty-second. Pep Guardiola grabbed his head like someone had suddenly turned the volume in his ears up really, really loud, spinning on his heel, rotating through 360 degrees and ending up right back where he had started. José Mourinho leapt from the bench pointing. Ronaldo stood, chest out. Leave it to me. As plans go, it's not a bad one: for the third game in a row, he had scored at Camp Nou. He has now scored in four of the last five clásicos. He also scored the winning goal in the Copa del Rey final last season.

"The league is his," ran one newspaper cover on Sunday morning. It was an exaggeration. After all, the goal that broke the league's all-time record, taking Madrid to 108, was scored by Sami Khedira. After all, Madrid were well-organised throughout; every man played his part. Xabi Alonso did not allow Lionel Messi space. Ozil was tireless. Sergio Ramos has become a commanding centre-back. Iker Casillas made a vital save when Xavi was one on one. And Karim Benzema never makes bad decisions. But it was also understandable: this season he has pulled Madrid towards the title. "He's called Cristiano and his surname is Ronaldo," cheered mad Madridista Tomás Roncero, quite wrongly. "The Ronaldo mug [yours for just 1.95 in today's AS] will be sold out in two hours," he cheered, quite rightly.

This was a game that Barcelona had to win if they were to have any hope of winning the league. From 10 points to eight, to six, to four, to one, all the calculations made one pretty significant assumption: Barcelona would beat Real Madrid. They didn't. It never really felt like they would here. And when at last, momentarily, it did, Ronaldo made sure they didn't. Madrid are seven points clear; the league title is theirs four years since they last won it.

When the final whistle went, Messi turned and disappeared down the tunnel without a word. He has now failed to score in the last four clásicos. Madrid's players turned to the few hundred fans high in the stand and punched the air; Pepe made a point of kissing the badge; Casillas meanwhile sought out Barcelona's Spaniards and embraced them. In the dressing room, Ramos took pictures of him and his team-mates – "sensitive content", said Twitter – and Alonso put on a bit of Belle and Sebastian. Guardiola walked into the press conference room, sat down and announced: "I would like to congratulate Madrid on this victory – and on the league."

At around the same time Madrid's players, showered now, returned to the pitch to applaud the fans, still waiting in an otherwise almost empty stadium. Crowds were already gathering at El Prat airport; cars were turning up at Cibeles, the fountain of the goddess of fertility where Madrid celebrate their successes. The players won't turn up yet – assistant coach Aitor Karanka couldn't even muster a smile as he insisted that there are still points to play for – but the fans did.

Madrid had just won the league but they had not just won the league. There was something more to this. It had to happen some time, but this was a kind of exorcism. They would quite likely have won the league if they had drawn or even lost – they would still have been four, or one, point clear with just four games to go. But had they taken the title without beating Barcelona there might have been something missing, something not quite right. Instead, this felt like they had really taken it from Guardiola's team; like their time had come. Last year's Copa del Rey mattered, of course, but it was always the least important of the three competitions in play. It immediately followed abdication in the league and was immediately followed by elimination in the Champions League. This was a more definitive statement.

It was not just about Madrid destroying the rest; they had beaten the best too. Mourinho won at Camp Nou for the first time. Ronaldo won at Camp Nou for the first time. And Madrid won at Camp Nou for the first time in four years. The inferiority complex finally washed away. Some of the bad memories too; in finally overcoming it, the trauma induced by Barcelona's success was revealed. "¿Dónde está, no se ve, la manita de Piqué?" chanted Madrid fans waiting for the team at Barajas airport. "Where is it? We can't see Piqué's hand." The hand in question was the one he raised after last year's 5-0. If that manita was the symbol of Barcelona's dominance, Madrid fans hoped that Ronaldo striking a pose symbolised its end.

Clásicos have a habit of giving way to sweeping, dramatic conclusions; they are epoch definers, even when they are not. Power shifts, eras end and obituaries are written, often with indecent haste. Football is a sport, losing happens. On Sunday, Xavi was quick to insist that Barcelona are only three games away from a historic season: they have already won the European Super Cup, the Spanish Super Cup and the World Club Championships and now they have a Champions League semi-final second leg to come and another Copa del Rey final. They have won 13 of 17 competitions under Guardiola. If a team deserves the benefit of the doubt, it is this one.

There is something a little cheap about joining the queue to attack Barcelona now; something opportunistic. There can be little reproach. They have scored 125 goals. They have been beaten to the league title by a fantastic team and they could still win five trophies this season. There is no reason to assume that they will collapse completely or that the league title changing hands heralds the end of this team. Equally, though, it does herald the arrival of Madrid and they could end without the league, Champions League or Copa del Rey; optimism becomes pessimism remarkably quickly. One of the reasons for that is that Saturday revealed failings too – some of which have been nagging away in the back of minds, even as Barcelona went on that brilliant run of 10 wins in a row. Small failings, barely perceptible ones most of the time, but ones that are there.

Guardiola wanted width, so chose Cristian Tello and Dani Alves. Tello was so far on the touchline that Barcelona rarely found him and, as Alves himself intimates, he is far more dangerous arriving in attacking positions than starting there. Building around Messi makes sense when you see his extraordinary statistics and the consistent brilliance of his performances but there are times, and Saturday was one of them, when there is a lack of variety and a lack of presence up front – there is no Samuel Eto'o figure, no Thierry Henry, no Zlatan Ibrahimovic and, because of injury, no David Villa either. Alexis too has suffered a string of muscle problems this season. Meanwhile, the three-man defence was vulnerable and the midfield four rarely connected in positions from which they could do real damage. Xavi, the man who makes it work, has needed protecting from injury.

The more Barcelona have focused on controlling the game, the less they seem to have been able to kill it. Against Madrid they completed well over 700 passes; Madrid completed just over 200. Madrid had six shots on target, Barcelona just three. All of Barcelona's passes matter, they are the building blocks that create their footballing edifice. They are an expression of non-negotiable style – the style that has got them where they are, proving wildly successful – but without the murderous intent there is something missing. As Juanma Trueba notes in AS, quoting the bullfighter Juan Belmonte "performing passes is not the same thing as bullfighting". "Likewise," Trueba notes, "playing the ball is not [necessarily] playing good football … trying to defeat Madrid that way is like trying to kiss a bull to death."

There is a small squad and fatigue too. "They have been working since August. You ask for the same as ever but there are times when, after playing for everything for four years, it's hard," said Guardiola. "I hoped that [moment] would not come against Madrid." Barcelona had played on Wednesday and again on Saturday (not Tuesday-Sunday), just as they had the last two times they had been beaten in La Liga: the loss to Getafe was preceded by Milan; the loss to Osasuna preceded by Valencia in the Copa del Rey. A few days ago, Barcelona announced that this summer they will not be going on tour but will instead stay in Europe for the whole summer. It is a response to the belief that Barcelona paid for their poor preparation. "Some teams have a pre-season, we had a tour," he noted then.

Guardiola's own doubts over his future cannot have helped; the illness to his No2, Tito Villanova; the concerns over Piqué.

This is a kind of footballing chaos theory. In a league where the points totals are so high, the tiniest mistake, the flutter of a butterfly's wing, has a huge impact. Draws are the new defeats; defeats are the new disasters.

Most significantly of all, Barcelona have come up against a hell of a rival. Of the four trophies that Barcelona have not won so far, three have been ceded to Mourinho – a European Cup against Inter, plus a Copa del Rey and now the league title. That is precisely why he was brought to the Bernabéu. The league is the title that, in theory at least, most defines which is the better side, even though it is the European Cup they both want above all, and fundamentally Madrid have won the league because they are extremely strong: the side that went to Camp Nou cost over €400m, and the work they have done under the Portuguese coach – analysed here – has been effective. They've scored more goals than anyone else in Spanish league history.

Madrid have succeeded in competing against the team many considered the best ever. Yet that equation can be turned on its head: Barcelona have competed against one of the most powerful teams ever assembled too. They have competed with each other, taking this to another plane. No one else has been able to compete with them, Valencia are 32 points off the top. Four years later, Madrid came out on top. This time, the lights went out on Barcelona. Something shifted in Spain on Saturday night.

Talking points

• Sevilla's match with Levante was delayed until 10.30pm on Saturday night, instead of occupying the normal 10pm slot, meaning that it finished well into Sunday. The reason was simple: so as not to clash with Barcelona-Madrid. But, you protest, Barcelona-Madrid kicked off at 8pm – it would be well finished by then. Ah, but this was designed to make sure that it did not clash with the post-match fallout from Barcelona-Madrid. "Stop the game," ran one banner at the Sánchez Pizjuán, "Mou's talking!" Sevilla fans, who have watched their side play in a lot of the least hospitable slots this season were hasta las pelotas. Literally, up to the balls. So they decided to show just how hasta las pelotas they were – by throwing hundreds of tennis balls on to the pitch in protest.

• Arda Turan. Woof! He scored two golazos as Atlético beat Espanyol 3-1. Both they and Athletic Bilbao are up to 48 points – just one off Levante and three off Málaga and in with a genuine chance of the final Champions League slot.

• Remember Ali Syed? Remember how he took over Racing Santander and celebrated in the directors' box when they beat Sevilla? Remember how he promised signings? Remember when he said that they would challenge Madrid and Barcelona? Remember? Racing Santander are down, 11 points from safety with 12 left to play for. As for Syed, he's disappeared.

• A point for Granada, a point for Villarreal … slowly inching their way to survival. Zaragoza and Sporting's grip on the first division loosens.

• Real Madrid played the world's best team this weekend. Real Madrid B, that is. And they lost too. But still won the league. Oviedo 1-0 Real Madrid Castilla.

Results: Mallorca 1-0 Zaragoza, Sporting 2-1 Rayo, Barcelona 1-2 Real Madrid, Sevilla 1-1 Levante, Granada 1-0 Getafe, Real Sociedad 1-1 Villarreal, Racing 0-1 Athletic, Atlético 3-1 Espanyol, Valencia 4-0 Betis. Monday night: Osasuna-Málaga.

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