They already blew up their chances at the top of the table, they had advantage over Barcelona and even tried to score two goals but lost concentration when they were supposed to hold onto their two goals lead in less than 25 minutes. Barcelona showed them who the boss is and took charge of the game. Very soon they will be having their rematch against same Barcelona but in the Copa Del Rey. If they win at least they will have their revenge and still have the opportunity again to face Real Madrid and possibly win them to lift the Copa Del Rey trophy this season.
Atletico Madrid need to play two semi final matches in Copa del Rey only because they need to win those matches and go to final match for taking a cup. They must avoid idea and approach of revenge as it can be very harmful for their preparation and approach in two important semi final matches. Barcelona in this season are very strong and have very good ability to bounce during hardest times, and if Atletico Madrid don't play two matches with highest concentration, they will be the loser.
They still have time to make things right if they can make up for their losses and try to win matches since they are out of the champions League, Atletico Madrid should have been at the top of the table should they had won against Barcelona when they were 2 goals ahead of them but allowing Barcelona to defeat them from 2 goals down was the beginning of the issue of Atletico Madrid and their chances of winning the league title slipping out of their hands.
It's a painful defeat for Atletico Madrid as in this season, there are not too many teams that managed to score and lead Barcelona with two goals. Atletico Madrid did it in an impressive way but they failed in securing two goal advantage and lost the match eventually.
Atletico Madrid facing Barcelona in the Copa Del Rey will be a big game but Barcelona is still stronger than them at the moment so I doubt if Atletico Madrid can defeat them before facing Real Madrid.
Atletico Madrid now have only Copa del Rey is a most possible title to win in this season. They were out of Champions League and their chance in La Liga is very low now. Copa del Rey is most possible title they can win but firstly they must win against Barcelona in two semi final matches. It's hard but with experience and lesson from a latest good match but defeat by Barcelona in La Liga, Atletico Madrid can learn something from it and improve themselves for two better matches in Copa del Rey.