First they became the only side to beat Barcelona, coming back from 2-0 down to win 3-2 with a 90th-minute winner. Then they won the last ever Basque derby at San Mamés, their captain leaving the stadium with a stone replica of the cathedral he had conquered at last to go alongside the match ball he took from the Santiago Bernabéu. Now Real Sociedad have become the only team to beat Atlético Madrid at the Vicente Calderón this season. Not just the only team to beat them: the first team to even get a point there. In fact, last night Real Sociedad became the first team to get any points at the Calderón since Real Sociedad got a point at the Calderón last season. And the impact could be huge.

Fifty-two minutes had gone when Antoine Griezmann sent Xabi Prieto running through. Standing before him, all in yellow, a man who had just broken a club record. Somewhere in the midst of that garish collage of adverts – Buy A Kia. Need a Taxi? Drink Coca-Cola. Eat meat – the clock on the stadium scoreboard ticked up to 34min and they started chanting. "Courtois! Courtois! Courtois!" The goalkeeper had just passed Abel Resino's record: he'd not let one in since October when Roland Lamah scored for Osasuna. Now, 33 minutes after the chant, five months and 819 match-minutes after he had last conceded, it finally happened again.

This time it mattered too. Lamah's goal was a solitary strike in a 3-1 defeat; Prieto's was a solitary strike, full stop. He slowed down and curled the ball under Courtois' body to put Atlético Madrid behind for the first time all season and there was no way back. At full-time, Iñigo Martínez clenched his fist and let out a roar. High in the stands, Real Sociedad's fans leapt up and down. Fourteen consecutive league wins later, in the week in which coach Diego Simeone had signed a new contract, Atlético Madrid had been defeated. The record gone, their place too. Real Sociedad had done it again.

Look at the table this morning and for the first time this season Atlético are behind Real Madrid, slipping from second into third. Look a little lower, but just a little, and for the first time this season Real Sociedad are in a Champions League place: fifth, level on points with fourth-placed Málaga who Uefa has banned from European competition next season. "This is great! It's a joy to be in this position," the captain Xabi Prieto insisted. "If you had told me at the start of the season that we would be there, I'd have said you were mad."

Hardly surprising. This is, after all, the first time that la Real have been in a Champions League place in a decade. In 2002-03, they were runners-up; since then they have not finished in the top half of the first division table. Three of the last five years have been spent in the second division. Their coach, Philippe Montanier, who joined a year and a half ago, seems to have been permanently on the verge of the sack or a fans' rebellion, supporters calling for his head, the club calling potential successors. And this season started with six defeats in the first 10. But Sunday's win was their third away win in a row, and since those opening 10 games, they have lost just one in 17 - and that was 4-3 at the Santiago Bernabéu, a game where for a long time, as one match report put it, "Real Madrid were a toy in their hands."

Within the club, most say that the turning point came away at Málaga in week 11. One first-team player talks about "correcting mistakes." That day, la Real took a step forward. Until then they had been a a la expectativa: they tended to wait rather than really go for the game, as if they did not fully trust in the talent their players held. . Certainly, that was the accusation levelled at Montanier and often quite aggressively too: his critics said he was too conservative. Media and supporters were not always impressed. Focus was trained particularly on Rubén Pardo, for whom la Real have already turned down a €6m bid from Real Madrid, and Montanier's apparent reluctance to include the player that most excited the fans.

Against Málaga, Markel Bergara and Elustondo were injured. Asier Illaramendi and Pardo played together. Victory followed, then another win at Valencia when they scored five. Pardo started that game too, albeit without Illaramendi. It is not as if they suddenly became super-attacking and nor did Pardo become an automatic starter – he has begun just nine games – but something shifted. The players stepped up, the atmosphere changed, the attitude. The belief. Prieto was switched from the right to the middle where he could influence the game more, combining with those around him, his relative lack of pace less of a problem; Vela began to play nominally on the left wing, a starting point from which to attack on the diagonal rather than finding himself stuck up front. The speed of their attacks was devastating: There are few front threes as swift as Vela, Griezmann and Chori Castro. Only three teams have scored more goals; no team has delivered as many passes into the area. Last week, they drew 3-3 with Betis at home.

Sometimes there is a tendency to over-analyse; sometimes the explanation is startlingly simple: la Real have very good players, most of them technically impressive. Go through them one by one and, judged purely on ability, few squads have so much talent. There are other factors but even those have to be judged in the context of a talented team. For eight games in a row they played against a man fewer, too, while Sunday night's goal should probably have been ruled out for offside. But if that run of red cards looked like luck, Griezmann insists it was quite the opposite: "red cards are not chance," he insists, "we have a lot of quality and a lot of pace and because teams cannot stop us, they end up fouling us."

Having started to win away, they began encountering ultra-defensive opponents at home, while at times it still feels like they need an out-and-out striker who guarantees goals. But there was greater variety about their game, more belief and creativity. And they are far more resolute, as Atlético found out to their cost, defeated at their own game. Montanier's work was taking effect – "I'm glad the results are starting to prove him right after everything that was said," one player insists – and they were also gaining in confidence and maturity, conceding fewer goals: Mikel Gonzalez has been a revelation at centre-back and Montanier has praised their ability to "suffer" and to defend intelligently. Against Athletic Bilbao they were overrun in the first half, one player insisting that a year ago they would have lost that match; on Sunday night the coach highlighted their ability to defend through possession and catch Atlético with speed.

Then there's the intangible. When they were relegated at the end of 2006-07, la Real were forced to turn to youth. That was the bad news; the good news was that the work being done at Zubieta was impressive and so – despite the greater financial muscle of Athletic Bilbao – was the scouting, the ability to bring talented players into the club. Important players have been signed – Claudio Bravo, Carlos Vela, and this season Chori Castro – yet of la Real's 23-man squad, 16 have played for Real Sociedad B. That tradition is not new but now an especially talented generation is coming through too, growing together: the central midfielders Rubén Pardo and Asier Illaramendi and the centre back Iñigo Martínez (who scored from inside his own half twice last season), all born after 1990, will certainly be Spain internationals in the next few years.

Now they talk about their stress on home-grown players as a philosophy, a matter of principle not price. Montanier was brought in, at least in part, because of the belief that underlying his success in bringing Boulogne up from the fourth division to the first was his handling of young players. At Real Sociedad, players describe him as "methodical"; he likes his team to have the ball and he likes to control every detail – asked recently if the players would be eating a big Basque steak to celebrate victory, he responded "watch the diet". He is strict but he has also shown a softer touch with younger players, insisting that they are still exactly that: young players. Within the squad they describe him as "calm", keen to develop young players but slowly, steadily.

The philosophy is about identity; this is a team that represents something: seven of their players were born in the province Guipúzcoa of which San Sebastián is the capital. Xabi Prieto, a Real Sociedad season-ticket holder from the age of five, did not leave when the team went down, even though his former manager Juanma Lillo insisted that he was good enough to play for Barcelona. He talks about the degree of commitment and collectiveness within the squad, which the players from outside of Guipúzcoa and the Basque Country embrace. "When we go out, there can be 15 of us all together," Prieto says. Arsenal have an option to sign Carlos Vela for €4m; he may not have any choice but he says he wants to stay.

It makes sense. Vela has scored 12 times this seasons and provided six assists, becoming one of La Liga's outstanding performers. Stay and next season he may get the chance in the Champions League. After 10 games unbeaten, that's the spot his side occupy this morning. The question is can they stay there? Asked exactly that, Prieto replied: "I don't know." It didn't sound like he thought they could. But then no one thought they would beat Barcelona. Or win the last ever derby at San Mamés. Or end Atlético Madrid's 15 game winning run.

Talking points

• Time was running out when Leo Messi, on as a sub, finally did what he does (in the league at least). Two minutes later the final whistle and Barcelona had done what they don't do. Messi dinked the ball over Dani Aranzubia to keep up his run of scoring in consecutive games and take him to 40 for the season, wrapping up a 2-0 win: the first time Barcelona had kept a clean sheet in two months.

• Want more evidence of Monchi's diminishing power as sporting director of Sevilla … and of the lingering power of goalkeeper Andres Palop? Check out Balaidos on Sunday, where Madrid beat Celta 2-1 in a game that could have finished 6-6 but for the goalkeepers, Javi Varas and Diego López. Two men who were at Sevilla six months ago, but weren't playing. Palop was. Sevilla's slow decline continues.

• Athletic: two wins in a row for the first time this season and pulling out of trouble. "I recently said that we had 20 points less than we should," Bielsa explained. "Now it's 14 because in the last two games, results [rather than the play] have gone our way."

• And could Manzano manage a miracle at Mallorca? They're just one point off safety after winning again. Against Sevilla. The goalscorer was Pablo Alfaro. Who began his career at Sevilla.

• Betis, meanwhile, are flying. And fun too. Along with Valencia, la Real (and Málaga, should Uefa lift the ban), they're genuine contenders for a Champions League place. Deservedly so, too.

Results: Real Betis 2-1 Osasuna, Rayo Vallecano 2-0 Espanyol, Valladolid 1-1 Malaga, Barcelona 2-0 Deportivo La Coruna, Mallorca 2-1 Sevilla, Levante 0-0 Getafe, Celta de Vigo 1-2 Real Madrid, Atletico Madrid 0-1 Real Socidad, Zaragoza and Granada play on Monday.

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