Atletico Madrid lost key points which cost them a lot this season, and with four points separating them from the league table, they did not seem to be a title candidate anymore. They lost to Leganes, who are at the bottom of the league, and the previous two weeks were against Getafe after Arambarri scored a brace in 6 minutes to help Getafe fight back. Even though one of Atletico Madrid's players was sent off, they still had the power to defeat Getafe, especially when they were leading by one goal.
They are still a candidate, one of three candidates for the title, but their chance will be better or worse depends on result of Barcelona match, the leader in La Liga now. If Barcelona win their match, they will difference in points with Atletico Madrid to 7 points, then it wil decrease chance of Atletico Madrid a lot and even eliminate Atletico Madrid from the title race.
I thought the game against Barcelona would be an opportunity for Atletico Madrid to bounce back from their Champions League defeat, but they were unable to maintain the advantage and conceded four goals in the second half after 2 goals lead. Atletico Madrid had three consecutive losses, losing two league games and being eliminated from the Champions League; they may recover this season, but they have lost their opportunity to compete in the league.
Atletico Madrid played well and did almost everything necessary to beat Barcelona and rescue their own chance in La Liga title race. Unfortunately, they are not strong enough to maintain good advantage of two leading goals, and Barcelona are simply too strong mentally to bounce back, not only rescue the match for a draw, but also make a comeback and win that important match.
They will continue their fight until they exhaust and fall behind farther than now, but it's still too early for them to give up this weekend or in next several match days.