The coach believes that the tie is finely poised and insists on Los Blancos attacking from the off, while Pepe and Luka Modric should be available to play.
Goals from Xavi, Lionel Messi and Pedro were enough for Tito Vilanova's men to edge out their arch-rival at Camp Nou last Thursday, but a late Angel Di Maria strike gave the Liga champion hope.
The Portuguese coach is certain that his troops are able to overturn the deficit if they put in the right performance, but stressed that he was not overly concerned with the outcome on Wednesday's match after a poor start to the club's Liga defense.
"Everything is open tomorrow," he told reporters at press conference. "Tomorrow we will try to defend whenever [Barcelona] have the ball and attack when we have it. We must try to score from the first minute. The team does not have to change anything from the way we played at Camp Nou. We had a good game.
"Winning the Supercopa and beating Barcelona is not important to me. My priority is knowing what happened against Getafe [on Sunday] - whether it's a psychological problem. What's important is knowing whether that was a one-off."
The capital club has yet to taste victory this season after the 2-1 defeat to Getafe, a 1-1 draw with Valencia and the reverse at Camp Nou, but Mourinho feels the team's performances have been impressive, the loss aside.
"The team deserved to win against Valencia, and they were better and more balanced against Barcelona, but the last match was unacceptable," he said.
Madrid has since added Luka Modric to the squad, and Mourinho is looking forward to the Croatian making an impact, and also confirmed that concussion-victim Pepe is available for selection.
"Modric was our first choice, and we know where he can play," eh said. "Modric's condition is normal for someone who hasn't trained with their team for a while. A player like Modric will be in good form soon.
"Pepe trained without any problems yesterday and his wife gave birth to their daughter, so he is better than ever. We hope that he can play tomorrow."
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