Diego Simeone clenched his fists and turned to the east, heading quickly down the tunnel and out of sight. Way up in a corner of the Santiago Bernabéu's north stand, fans in red and white embraced. Only 70 of them had made the eight and a half kilometre journey across town, 30,000 fewer than last time. Ticket prices had been as high as their seats and, besides, they'd already lived the moment. Nothing could ever match that again. Not even this, although this was pretty damn good. They didn't party like it was 1999 or even May 2013 but Saturday night was historic: for the first time this century, Atlético Madrid defeated Real Madrid in the league.

It had taken Atlético 14 years and 25 matches to defeat their rivals at all and blow that fatalism away for good, to start a new life, glimpse a new dawn. A real one this time. Now, as if to prove the point, they had done it again just four months later in the very next derby. Another night, another Atlético victory. Diego Costa's first-half goal was enough to secure a 1-0 win. For the first time ever, Atlético had won two consecutive games at the Bernabéu: the last time they had won two consecutive games at Real Madrid was in 1920 and 1921, when they played at the Campo de O'Donnell.

There were lots of ways of reading this, lots of 'explanations'. Maybe it was all about Iker Casillas, the captain sitting on the bench: since he made his Real Madrid debut, he has started 24 times against Atlético and not lost while of four times Real have started without him, they have lost three.

Maybe it was the press's fault: the first chant of the night came from the South end and ran "Media hands, out of Madrid!", although it could be just as easily turned on its head. Or maybe it was all Wales's fault. After all, the last time Atlético beat Madrid, Real's manager was John Toshack. Soon after he was sacked. Fourteen years went by without a league defeat … and then Gareth Bale made his home debut.

Or maybe it was just Madrid's fault. Neither system nor style is yet clear, they are missing Xabi Alonso and Mesut Özil. Sergio Ramos and Pepe are good players but not always a good partnership, and the warnings were there. There has been another sea change. Since 2009, Atlético have won five trophies to Real's three.

Real have turned to yet another new project but that project still needs to be defined and perfected. That takes time but, in the league at least, time is not something they really have. This morning they sit five points behind the league leaders, Barcelona, and after the penalty they were gifted in the 95th minute at Elche in midweek, it really should be seven – half as many points as the champions have dropped in the whole of the past two seasons.

Or maybe there is another reason: Atlético. Maybe there's a simpler explanation: logic. This was the right result. Right now, Atlético are a very good side, a better team than Real Madrid – and 'team' is the word. "Millions 0 Football 1" declared the cover of AS on Sunday morning. "They're a great team and they will be up there," Ramos said. Marca's headline declared: "The best Atlético in history." Which is statistically true, but Atlético were having none of it. When Simeone headed straight down the tunnel, it felt like he did so in order to celebrate away from the cameras, to contain his joy. It was as if he wanted to avoid externalising the euphoria.

This was a huge result and yet there was something understated about the response. On Sunday morning, 200 supporters turned up at the club's training ground in Majadahonda, but they did not gather at Neptune's statue, their symbolic celebration site, again. "A final is better than anything, but we read this game very well," Simeone said. "I'm calm: the season is a long one." "Can you win the league?" he was asked. "It would be demagogically perfect for me to say that, yes, now we can win the league but I'm not going to," he insisted. "This doesn't change anything." Outside in the Bernabéu mixed zone, Koke admitted: "Yes, we're candidates … candidates for the next game."

Simeone's rationale made sense while Koke's response encapsulated their attitude. Simeone has talked often this season about how winning the league is impossible. Here, he spoke again of the economic potential of Madrid and Barcelona and as the season progresses the strength in depth is likely to make an impact. Winning the league probably is beyond Atlético. Last season they were seven points ahead of Real Madrid in January but eventually finished below them. Injuries will do them damage. They will not lose often, but every draw will cost them two significant points in a league where the champions may reach 100 again. Simeone has insisted, too, that in any given season one of the big two might falter but not both. Proof comes in the fact that while Madrid have dropped points already, Barcelona have won every game.

But then so have Atlético. It was not just that Atlético defeated Real Madrid on Saturday night, it was that it saw them complete the best start to a season in their history – seven wins from seven. Win next weekend against Celta at the Calderón and it will be the first time any team have ever won the opening eight matches of a league season (although Barcelona could match them with a win against Valladolid at home).

This has been building: Europa League winners in 2012, then Copa del Rey winners last season. This season Atlético won their first Champions League match against Zenit St Petersburg and they only lost the Spanish Super Cup on away goals after two draws against Barcelona. In other words, over their last four matches against the big two, they are unbeaten; in other words, they are unbeaten in 10 competitive matches this season. Eight wins, two draws. They have gone 16 games on the road without defeat. And now they sit five points ahead of Real Madrid.

It is no fluke. Saturday's victory was a reflection of what Atlético are, of how they have played so far. "They deserved to win. Yes, they can win the league," Carlo Ancelotti said. For the goal, Koke's clever angled pass found Diego Costa, who finished brilliantly. The league's top assist provider and joint top scorer had combined again: Costa has eight goals, Koke six assists. Of Costa's last 17 goals, 11 have been provided by the 21-year old midfielder.

There could have been more. Costa found himself one on one but Diego López saved. David Villa unusually chose not to volley first time after Koke found him with the outside of his foot. Arda Turan scuffed his shot from the edge of the area. López saved Gabi's header, Koke hit the bar, Thiago hit a post. At the other end, Thibault Courtois only made one truly outstanding stop, from Álvaro Morata's acrobatic volley. No goalkeeper in La Liga has been forced to make so few saves: coming into this weekend both López and Víctor Valdés had made twice as many.

Before the match, Ancelotti insisted: "Atlético Madrid play like Diego Simeone played: tough, focused, and tactically perfect." They are evolving too. This season they are creating more chances and the confidence is clear: they are happier to keep the ball and work their way out of trouble. They are not just the aggressive, defensive, counter-attacking team that some would claim: they came into the weekend having already scored more than Real, too.

Under Simeone, every single player has improved. Miranda silently continues being arguably the best central defender in Spain. Gabi reads the game like few others; tactically astute and always alert. Turan is a player of class and character. Villa has stepped into a supporting role and done so without complaint. Koke has been a revelation, creative, clever and adaptable. Diego Costa, who was already becoming the side's most important player last season, even while Radamel Falcao was still there, is possibly La Liga's best player this season and the more important he feels, the better he gets.

His movement is varied and clever, his timing impeccable. He was also involved in every battle, as usual. And here it's worth adding that on Saturday night, he was right every time: when he rolled on the floor, Álvaro Arbeloa had trodden on his calf; when he confronted López, the keeper had kicked him in the back; when he protested his yellow card, his foot was nowhere near as high as Ramos's head was low, and nowhere near connecting either.

The transformation under Simeone has been extraordinary. He has made the cliches true: watch Atlético play and the constant insistence on commitment, hard work, the collective makes sense; it does not sound like meaningless manager speak. "No one is more important than the team," the manager said. Now, though, there is another layer to what he says, more of a glimpse of the thought process, the study, that was always there but not always expressed. "We interpreted the game very well," he added. This is a mature, intelligent team, aware of its qualities, and of its limitations.

Above all, Atlético are a side who know exactly what they are doing: their identity is clear, and they believe in it. They are emotionally stronger, afraid of nothing, never shirking a challenge. The Copa del Rey final was symbolic, the confirmation and reaffirmation of a shift in their mentality, a physical, tactical and psychological process that Simeone had already begun. "We took the pressure off ourselves winning the Copa del Rey," admitted Gabi. That win, 17 May 2013, was the first day of the rest of their lives; the most striking thing about Saturday was that it almost felt like just another day. Another deserved victory.

In the last minute of the derby, Courtois almost dropped the ball at the feet of Gareth Bale. It would have been a very Atlético way of blowing it but for one thing: that's not the Atlético way any more.

Talking points

• Leo Messi scored another lovely goal but was also taken off with another muscle injury – a recurring theme once again post-Guardiola. He will be out for two to three weeks. Which, given that there's an international break coming up, might not be a bad thing.

• "We slit our own wrists every day, Rayo Vallecano's coach, Paco Jemez, announced before his side's trip to Valencia. "No one hurts us as much as we hurt ourselves." The good news for Rayo was that they only conceded one this time; the bad news is that despite dominating possession once again and racking up 14 shots to Valencia's five, yet another mistake cost them a goal and cost them the game. They are bottom of the table on just three points. They have conceded 21 times already – more than anyone else in Europe's top leagues. Next up, Real Sociedad.

• Goal of the week? Pawlowski. Brilliant. Miss of the week? Trochowski. Whoops.

• Dodgy refs change games, again? Osasuna 0-1 Levante, Betis 1- 0 Villarreal, Real Sociedad 1-1 Sevilla.

Results: Valladolid 2-2 Málaga, Valencia 1-0 Rayo Vallecano, Almería 0-2 Barcelona, Real Sociedad 1-1 Sevilla, Real Madrid 0-1 Atlético Madrid, Osasuna 0-1 Levante, Celta 0-1 Elche, Espanyol 0-2 Getafe, Real Betis 1-0 Villarreal

Monday night: Granada v Athletic Bilbao

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