Real Madrid manager Jose Mourinho admitted conceding an equaliser from a corner "deflated" his side as they went on to lose 2-1 to Barcelona in the first leg of their Copa del Rey quarter-final at the Bernabeu.
Cristiano Ronaldo had given the hosts an 11th-minute lead, but Barcelona levelled when Carles Puyol was left unmarked to head in Xavi's corner before Eric Abidal struck the winner 13 minutes from time.
"We were winning 1-0 and that is a great result at home in a two-legged tie, but then we concede a goal from a dead ball and you cannot do that against a side with the quality of Barcelona," Mourinho said.
"After that it is normal that our players were a little bit deflated and their players get a great boost from a goal just after half-time, and that was the key to the game."
Mourinho refused to be drawn on Pepe's behaviour after the Portuguese defender appeared to stamp on the hand of Lionel Messi while he was on the ground.
"I haven't seen it, but obviously if it is deliberate he will be punished," Mourinho added. "What I can say is that he did a great job for the team."
Mourinho still believes his side are capable of turning the tie round in the second leg at the Nou Camp.
"It will be extremely difficult but the tie is still open," he added. "The league remains the priority and now we have to concentrate on a difficult game against Athletic Bilbao, but I am not going to admit defeat."
Barcelona manager Pep Guardiola was understandably delighted with his side's performance, but warned that they still have work to do to reach the semi-finals.
"The important thing for us was that we came with the intention to score and to score away from home is important," Guardiola said.
"We reacted well to going behind and to win is always a good feeling, but we have only played half the tie and Madrid is capable of anything. Now we must rest and prepare for Malaga and then the return leg."
Barcelona have now gone seven games unbeaten at the Bernabeu under Guardiola, including five wins, but the Barca boss does not believe he or his side have a mental edge.
"For us it is always a pleasure to come to the Bernabeu, the world is watching us and we know every time we must do our best," he added. "Tomorrow we must recuperate and prepare for the league because Madrid are five points ahead of us.
"However, I don't believe we have an edge over Madrid because they will have opportunities to win. It is true that we are playing very well, but in any free-kick, corner or piece of brilliance from Ronaldo they can score.
"They are averaging four goals a game. We have done our job very well tonight, but half the work remains to be done."