Coach Carlo Ancelotti says Real Madrid were punished for reverting to long balls in the 2-1 defeat by Barcelona.
Barca now lead La Liga by four points thanks to goals by Jeremy Mathieu and Luis Suarez.
"We played well for the first hour, but the last half hour was terrible," said Ancelotti of his side, who drew level through Cristiano Ronaldo.
"It is a blow, but we won't give up. We lacked a cool head to try to equalise rather than playing long balls."
He continued: "We played a lot better until the second goal. After that it was very difficult.
"In the first half we played very well, we had control, were dangerous up front and solid at the back."
European champions Real, who were four points clear on 27 February, have 10 games left to overhaul Barca's lead.
To do so, they will have to rediscover their form, having dropped eight points in the last four league games.
"It's more difficult, but we're not going to prioritise the Champions League," said Ancelotti. "The priority is La Liga and the Champions League.
"Cristiano Ronaldo played a very complete match. He worked hard and was always dangerous up front. He shot dangerously, he hit the woodwork... It was the same Cristiano as always."
Real defender Sergio Ramos said: "We gave our all but we lacked luck in the first half, and they controlled the game better after that.
"The difference is only four points and we are going to keep fighting in the league. We will not ease up."