Thibaut Courtois said Real Madrid lost control in their home loss to Girona that leaves Los Blancos nine points adrift of Liga leaders Barcelona.
A run of five straight wins, including last weekend's 3-1 defeat of city rivals Atletico at the Wanda Metropolitano, had thrust Madrid back into the title race ahead of the Clasico on March 2.
Casemiro's header put the hosts on track to extend their streak before Girona produced a stunning second-half comeback at the Santiago Bernabeu on Sunday, however.
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After Sergio Ramos was deemed to have blocked a shot with his arm in the box, Cristhian Stuani beat Courtois from the penalty spot to score his 13th La Liga goal of the season.