Samir Nasri has finished training, his heart monitor laid on the window ledge with the others. The scans say he shouldn’t play but he says he will and his manager appreciates it. He’s perhaps La Liga’s best midfielder so far; the man his coach says makes the team breathe. Steven N’Zonzi, perhaps the second-best, ambles by in flip-flops and baggy shorts. Lifesized inflatable footballers lean against the fence; actual footballers ride buggies, alighting at the gym. Sergio Escudero grins and staff embrace him. News just in: he’s in the Spain squad. The groundsman, in cricketer’s shirt and sunhat, takes corners wide on his lawnmower. Alongside, a stand is being built; the B team play here and they’re second in Segunda, occupying a prohibited promotion place. As for the first team, they’re just three points off the top.

Friday afternoon at Sevilla’s Ramón Cisneros Palacios training ground with its giant billboard showing Jesús Navas and Sergio Ramos holding the World Cup and there’s optimism – lots of it. There’s whitewashed walls and it’s lived-in enough to feel real, not sterile and sanitised – laundry room in one corner, a couple of those pump-up players lie on the floor like casualties, air slowly escaping. Yet they’re the only thing about this place that’s deflated. Fourth domestically, virtually through in the Champions League, delighted to be denied a defence of the Europa League title they have won three years running, life is good. Sevilla are playing well and winning sooner than expected, the sporting director admits. “We thought the adaptation would be slower,” Monchi says.

His manager disagrees: “you always have that hope,” he has said. But, then, his manager is Jorge Sampaoli, an optimist and enthusiast whose influence is felt here, a man who laments footballers becoming “functionaries”, preferring them to be “artists”. He wants them to enjoy this. If at first the play wasn’t entirely convincing, the ideal remained and the results sustained them; now, they have both. They’ve won every home match and even managed to win away, a year later. They’ve lost just once – at San Mamés – and they beat Atlético Madrid whose captain, Gabi, claims they’re candidates for the title. Deep down, Sevilla’s players don’t think they are – then again, Gabi didn’t think Atlético were in 2013-14 – but they are indeed enjoying this.

Defeated at the Etihad without Gerard Piqué and Andres Iniesta, and not at their best, Barcelona are next at the Sánchez Pizjuán and some even consider Sevilla favourites. They’ve won five out of five and scored 17 there. Since the Super Cup, there’s been just one game when they’ve had less of the ball then their opponents – away at Juventus – and that was by just 1%. “It’ll be difficult,” the Barcelona manager Luis Enrique says. “They’re going to suffer,” Sevilla president José Castro says proudly. He invites the cast of Game of Thrones to see it; a game approached with anticipation, rather than anxiety. Friday, two days away, and there are smiles, chats, warmth, enthusiasm. Why shouldn’t they win?

Here’s why not, one member of the coaching staff confides: “If he has one those moments.”

He is Leo Messi. And he does. Asked if he could explain his footballing identity a fortnight ago, Sampaoli said: “Yes. Don’t be scared. Don’t wait. Think more about their goal than your own. Want the ball. Go for it.” That ball is yours: when it’s not, get it back. A five-second limit accelerates that. He is totally different to Unai Emery, Nico Pareja admits: attack, always. Don’t wait, dominate. There is a word Sampaoli uses a lot which others don’t, expressing something about his idea: someter. It doesn’t translate that well, but it’s in the vein of conquer, subjugate, impose, subject. He wants his team to impose itself on its opponents – to overrun them. His Chile team was perhaps the ultimate expression: a stampede, charging forward fearlessly.

When Sunday came, Sevilla did the same. Their first shot came after 34 seconds, their second after 48. On 1.21, they had their third. Seventeen seconds later, Barcelona had their first, breaking through the pressure. It was rare that they did so, the waves more often crashing into them. Sevilla stampeded. Escudero volleyed wide. Vitolo’s shot was blocked. Then Vitolo scored. 15.02, the clock said. Sevilla had gone from one end of the pitch to the other, screeching through the space. One-nil and, it seemed, with more to come.

Quicker and quicker they went. Higher, too: cornering Barcelona, often quite literally squeezed into the smallest space by the corner flag and the fans – no way out. Pablo Sarabia was played in, but tried to lay it off with a backheel. Then he had a shot blocked. Vitolo put another one wide. Sevilla tore into their opponents. This was someter, right there. An attack ended with one full-back delivering for the other. Sevilla were flying: Mariano, Vitolo, Luciano Vietto, Escudero – all of them, in fact. N’Zonzi and Nasri controlled; Barcelona, the team once defined by its midfield, didn’t have a midfield: it was all they could do to watch Sevilla go by, too fast to be stopped. It was breathless and brilliant. Samuel Umtiti resisted. The shots racked up: seven to two. The ball was theirs, against Barcelona. The lead, too.

And then, with three minutes to go until half-time, Barcelona broke and Messi scored – gently, subtly sidefooting past the keeper – and something shifted. Something? Everything. Messi, above all. “That was decisive, emotionally,” Sampaoli admitted. Suddenly, Messi was everywhere. “We have a plan for Barcelona and another for Messi,” the Sevilla manager had said before the game; for 40 minutes it was successful, a minute later it was in pieces. Why didn’t the plan to stop Messi work, he was asked. “Because sometimes Messi lets you stop him and sometimes he doesn’t,” Sampaoli said. “When the game breaks [open], he’s unstoppable.”

The game broke open. Space appeared as Sevilla tired, unable to maintain that pressure, and Barcelona took control, even if control was never complete and the match remained alive until the last. From Neymar’s chance after 92mins, Sevilla went racing up the other end and could have equalised, the Pizjuán appealing for a penalty and complaining when only three minutes were added. Not just the Pizjuán either: everyone bar the shattered players wanted this to go on for longer. When the final whistle did go, with the final score 2-1 to the visitors, there was delight and relief for Barcelona and a kind of sad satisfaction for Sevilla. They had been brilliant even if they had been beaten.

Luis Enrique’s side, meanwhile, had responded superbly, amid the doubts. He described the game as “lovely, intrepid, between two teams that take risks”. It was also an important one, huge for his side. He insisted that it was a “deserved” one, too.

Denis Suárez produced his best performance since returning in the summer, passing his way into the match; Neymar ran at Mariano, easing the pressure at key moments; Sergio Busquets eventually got back on the ball, slowing the game down; Umtiti and Javier Mascherano sped about, putting out fires; Luis Suárez scored the winner. And Leo Messi, well, Leo Messi did everything and was everywhere.

Luis Suárez’s goal for Barcelona shortly after the hour mark ultimately proved decisive as his side came from behind against Sevilla. Photograph: Jorge Guerrero/AFP/Getty Images

Sevilla’s coaching staff always knew he might do something like this. They’d seen it before, after all. But even they didn’t expect something quite this good.

There is a cliche that gets trotted out endlessly when a less well-known player does something wonderful: if Messi had scored that we would be banging on about it for weeks. It’s not true; in fact, at times it feels like the opposite is true: Messi has made the remarkable so routine that it stops being so remarkable. It’s just him doing what he does. There’s not much new to say; all the good words ran out some time ago. Even swearing won’t do now.

They say you could get a thousand monkeys on a thousand typewriters and they would eventually come up with the complete works of Shakespeare. Maybe, but you could get a thousand monkeys on a thousand typewriters – God knows, the Spanish sports media have tried – and they still wouldn’t come up with much that was new to describe Messi. Pep Guardiola was right when he said: “Don’t write about him – watch him.” Yet this time was different. Messi scored the goal that changed this game – so far, so standard – and then, even by his own standards, produced a second half performance that was absurd. Ludicrously good. So good as to warrant talking about for once, maybe even writing about. He’d scored one and assisted one; but for wasteful finishing, he could have scored three and assisted three. One of them, dribbling through a space that wasn’t there, would have been among the best two or three goals he has ever scored. If Messi had done that, we really would have been banging on about it for weeks. We may well go on about this display for weeks anyway. Perhaps even for years.

With the Game of Thrones cast up in the stands, the puns in the papers were inevitable: kings, thrones and majesty were all over the place, empires and ruling too. Perhaps the most telling was the quote from Lord Varys that made it into the media: “A very small man can cast a very large shadow.” Messi is a small man, but El País called him “gigantic”. He passed, dribbled, controlled: he dominated and defended, deactivated opponents and activated team-mates. He cast a shadow over this entire game. A shadow? Light, more like. Usually seen playing at his own pace, this time he was hyperactive and he was everywhere. A No10, No4, No9, No7 and No8 in one: Messi, Xavi and Iniesta. “He can play anywhere,” Luis Suárez said. “Messi ‘Distefanoed’ Sevilla,” AS claimed.

That is some statement. There may be no player who has ever impacted on the club game like Alfredo Di Stéfano, the man who was everything. As his team-mate Amancio Amaro put it: “He was a defender, a midfielder and a striker. He was a fucking robot!” L’Equipe called him “L’Omnipresent”. Helenio Herrera famously remarked: “if Pelé was the lead violinist, Di Stéfano was the whole orchestra.”

“Messi is football, football is Messi,” one headline claimed. “I’m not saying anything new: Messi is the best player in history,” Vitolo said last night. “No one is like Messi,” Luis Enrique insisted. The Sevilla president José Castro called him “an extraterrestrial”. Asked to explain the result, he said: “They have Messi and we don’t.” Castro looked exhausted – they all did. Yet they had been exhilarated too. We all had. “I’m obsessed with people leaving the stadium with a smile on their faces, having seen a team play with no inferiority complex and no fear against Barcelona,” Sampaoli had said. They saw that. They also saw Leo Messi.

Results: Celta Vigo 2-1 Valencia; Espanyol 0-0 Athletic Bilbao; Granada 1-1 Deportivo La Coruña; Las Palmas 1-0 Eibar; Málaga 3-2 Sporting Gijón; Osasuna 0-1 Alavés; Real Madrid 3-0 Leganés; Real Sociedad 2-0 Atlético Madrid; Sevilla 1-2 Barcelona; Villarreal 2-0 Real Betis

Talking points

• Two belting good goals and two men might decide Gus Poyet’s future. Betis were beaten 2-0 by Villareal with goals from Roberto Soriano and Trigueros, leaving them just two points above the relegation zone and their manager on the edge. Last week fans chanted for him to be sacked; this week at least he avoided that away at the Madrigal but he is under no illusions. “Having a job depends on two people: the person who offers it and the person who takes it,” he said. “Not having a job is the same. No one knows what will happen tomorrow, or the day after.”

• Carlos Vela’s face said it all. He looked like he had been told a particularly good joke just before he went to do the touchline interview and seemed to be trying not to crack up all the way through, a huge smile seeking to escape, but just about kept under control. Obvious, perhaps, after his Real Sociedad side defeated Atlético 2-0, with two penalties, one of them coolly finished by him, the other scored by Willian José. And yet it was more significant that it might seem. For some time, Vela had disengaged and seemed disinterested. His recovery is hugely important for the side. Eusebio seems to have reached him in a way that others have not – and, yes, that does mean David Moyes in particular, but not only him. Real Sociedad are flying: they’ve won every game since the Basque derby in mid-October.

• This is Atletico’s worst start under Diego Simeone. Which seems odd when they’ve played better than before. But the explanation might be more simple than it seems: the fixtures. They have already been away to Barcelona, Celta, Real Sociedad, Sevilla and Celta. Next up, Real Madrid at home.

• Saturday’s afternoon games featured four goals – all of them penalties. The most controversial was for Las Palmas, who won 1-0 in the 94th minute after a tumble that looked suspiciously dive-y. And Osasuna felt very hard done to as well, Alavés getting a doubtful penalty quarter of an hour from the end. But it wasn’t all bad. Friday night gave us another 3-2 to start the weekend off and Sunday night in Seville was a great way to end it.

• Gareth Bale graces the cover of Marca and AS this morning, after Madrid eased their way to a not-always-that-impressive 3-0 win over Leganés. He is, they say, the new leader of a team that has now gone 28 unbeaten. But this week it is Ronaldo who has signed a new contract.

• Valencia are the only team in Spain without a clean sheet this season. But it’s worse than that: they have now got just one clean sheet in 39 games, spread across five different managers. This week, they were beaten 2-1 by Celta Vigo thanks to one from John Guidetti and a beauty from Facundo Roncaglia. The relegation zone is just one point away.

• Time to start talking about the second division, then?