I was really shocked after the result. Atletico Madrid managed to beat Barcelona away in the La Liga after 18 years...

It isn't a win at Camp Nou though but anyways.
I think the turning point of the game was Raphinha's lob shot hitting the upper post. If he scored there, Barcelona were going to make it 2-0. I think Atletico Madrid wouldn't manage to come back from that.
After that Simeone did his magic somehow again. A last minute winner brought the 2-1 win to his team.

I don't remember exactly but it must be like their 13th or 14th goal that came in the stoppage time this season. They are really in this title competition.
The difference in expected goals is noteworthy. For Barcelona it is 2+, and for Atletico it is 0.2+

Crazy, isn't it?
But nevertheless, this is a logical result if you look at how the teams are performing in recent games. By the way, Flick's percentage of losses is now 25% with Barcelona, which is almost twice as bad as Xavi's, who everyone (including me haha) so harshly criticized and called a weak coach.