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.