Firstly, it was the first time Diego Simeone had defeated the Catalan giants in a league fixture; he had achieved the feat in cup competitions before, but never in La Liga.
Secondly, they did so without their new arrival Luis Suarez, who had to sit out the meeting with his former club following the contraction of coronavirus while on international duty with Uruguay.
And thirdly - and perhaps most importantly - it was in the ease and the control in which they did it. Because, in reality, Atletico were able to play within themselves and defeat Barcelona, in the process moving a huge nine points clear of them in the table and making it clear that they are here for the long haul.
In a season where league conventions are being upended due to the coronavirus, the schedule, and increased injury lists, nowhere is this more obvious than in Spain. Real Sociedad, Atletico and Villarreal lead the way and deservedly so. We are seeing Real Madrid and Barcelona absolutely stretched to the limit and it is playing into the hands of their rivals.
Consistency has so often been a problem, but Atletico seem best-placed to sustain that across the season. Since back-to-back 0-0 draws with Huesca and Villarreal, Atleti have won five in a row domestically, putting them in a superb position.
There are so many things currently going right. Luis Suarez has slotted in seamlessly, while Simeone seems to have a hybrid 4-4-2 that works increasingly well with his line-up. And Joao Felix's promise being crystallised in on-pitch performance has been a delight to see.
Add in the dynamic duo of Koke and Saul in midfield and you have all the very best elements of a good Atletico team. Two goals conceded in eight matches, the solidity their success has been built upon, but they have weapons in attack now that a clear upgrade on Diego Costa and Alvaro Morata. It's exciting.
And despite Real Madrid's problems - their 1-1 draw in Villarreal made it just three wins in eight in all competitions - Madrid are infinitely better at grinding out results, particularly on the road, than Barcelona are and the gap between the Madrid clubs and their Catalan rivals is already significant.
Put simply, Barcelona are in no position to challenge for La Liga, or indeed any other competition this season, and this looks set up to be a title race between the capital clubs.