The home side felt hard done by the referee's decision to dismiss Pepe halfway the second half and Madrid's sporting director has labelled the incident 'decisive'
"The decision was quite rigorous and turned out to be decisive. It looked perhaps a harsh challenge, but he [Pepe] didn't have any bad intentions. He just timed it wrong," Valdano was quoted as saying by AS.
"I was really surprised that he [the referee] gave a red card. That moment changed the game. The referee's decision to sent Pepe off was the only thing that influenced the game more than [Lionel] Messi's role."
Valdano then looked ahead to the second leg of the semi-final tie and he refused to rule out a comeback for Madrid.
"A comeback certainly isn't impossible. We'll have 11 Madrid players on the pitch again, and we will show a great fighting spirit and won't give up. We will play to our own strengths in a way that characterises this club."
Both sides meet again at Camp Nou on Tuesday May 3.