The Blaugrana overcame Mourinho's side 3-2, recovering from a goal down at Camp Nou, leaving the Catalan giants favourites to win the first trophy of the season.
The Blaugrana had to recover from falling behind to Cristiano Ronaldo's header, and Xavi praised Barcelona's ability to get back into the match. Speaking to the press, he said: "We started the game well, but showed character to get back into the match.
"We had a great game, and to win was significant as it means we know what we have to do at the Bernabeu. If we play the same in Madrid [as we did at Camp Nou] then we will win the title."
Xavi also had words of encouragement for Victor Valdes, whose blunder late in the game at Camp Nou gifted Angel Di Maria the simplest of goals to leave the match in the balance at 3-2 in Barcelona's favor.
"Victor [Valdes] is a professional and the best goalkeeper that we could ask for," added Xavi.
Both Real Madrid and Barcelona return to Liga action at the weekend, before the two rivals commence battle at the Bernabeu on Wednesday.