Real lost 1-0 at home thanks to an injury-time goal from Antonio Sanabria.
"In the end a goal was scored against us that we did not deserve," said Isco.
"We are not experiencing things like last year. We are at the beginning of the season and we have time to reverse the situation. In the less good times we will continue being positive and we will fix this.
"It's true that it seems that if we do not score early in the Bernabéu we get anxiety. We have to improve that."
On Barcelona's seven point lead, he added: "Now at seven points it is true that we have to give a push, to tighten more and it is true that it is difficult.
"We are Madrid and we have to go for everything."