Appearing at a news conference recorded by dozens of television cameras at the Catalan capital's tennis club, Sandro Rosell of Barca and Real's Florentino Perez said they hoped the match, which will be watched by millions around the world, would be a festival of football.
The pair, who preside over the world's two-richest clubs by income and ended the news conference with a hug, were speaking after a small group of radical Barca fans hurled missiles at the Real coach as it arrived at the team hotel late on Sunday.
A Real spokesman said one object, probably a stone, had struck a window near to where defenders Raul Albiol and Alvaro Arbeloa were seated. The window did not shatter and the players were unhurt.
"I hope that tonight we see a great spectacle and a lot of fair play," Rosell said, before urging the Barca fans to focus on supporting their team.
"We have to send a message to the whole world that two great rivals like Barca and Real Madrid must dedicate themselves to playing and showing that soccer does not divide but unite."
Perez, whose unbeaten side are a point ahead of second-placed Barca in the La Liga standings after 12 matches, added: "It's a day of celebration. Two of the best teams in the world meet today and it's a match that attracts all soccer fans around the world.
"We will respond accordingly, not only with fair play but also by playing good football as we are obliged to."
Rosell, who is set to experience his first "Clasico" since taking over from Joan Laporta as president, sought to play down the importance of the game to the title race.
"It won't be decisive by any means," he said. "Whoever wins tonight will not be champion as there is a lot of the season left and there are other teams, not just Barca and Real."
