Madrid's defeat leaves them now 11 points behind Barcelona.
Pardeza remarked: "It was very demanding game, Betis subjected us to great work and we didn't have the luck we needed. As if that weren't enough, there was a legal goal that could have changed the course of the game and I was also told that there was a Betis hand in the area.
"These are circumstances that did not help us. Our duty and our commitment are to keep fighting. Real Madrid is not going to give up because of this defeat, because it has never done so at any point in its history."