Definitely a quite interesting result without a doubt. It has to be said that ATM played well enough to deserve that win and it wasn't just some lucky game. It happens, Real is not unbeatable team, they will of course have some losses all season long, I bet they will have more than this too, but not like crazy amount, maybe 4-5 at most and that would be normal for a regular season.
Yes, of course Atletico Madrid's victory in the match against Real Madrid yesterday was not just luck. Even though in ball possession they lost to Real Madrid, they were able to really optimize their attacks into goals. Of the 4 shots on target, 3 of them became goals. On the other hand, Real Madrid, from 5 shots on target, only scored 1 goal. From here it can be seen that Atletico Madrid's front line is really able to optimize the accuracy and effectiveness of their attacks which they can get from smaller odds. Meanwhile, on the other hand, Real Madird really needs a top striker so that their players or front line can be really sharp again.
Just because they lost this, doesn't mean that they are doing badly, they are going to get better hopefully from here on out with Vini playing at 100% as well, that should be a good thing for them. Barcelona is the one that must be happiest about this, Real is their biggest rival so them losing a game benefits them the most.
Yes, this defeat does not mean that Real Madrid is a bad club. However, from this defeat, Real Madrid, including Ancelotti, really learned a lot, the tactics they used and the strength of their current squad which lacks a sharp front line. They should be fully aware that with their current strength, it is possible that they will not be able to compete more strongly in the Champions League later.