United manager Sir Alex Ferguson was watching from the stands at the Nou Camp on Tuesday when Real romped to a 3-1 semi-final second leg victory, helped by a double from the outstanding Cristiano Ronaldo.
Real reached the May 18 cup final coming back from a 1-1 home draw, the same result United achieved at the Bernabeu in the first leg, to triumph 4-2 on aggregate with a commanding display against their arch-rivals.
Despite an inconsistent league campaign which has left Real third, 16 points adrift of leaders Barca, they proved they could rise to the occasion when required and batter a side who have beaten United twice in European Cup finals in recent seasons.
"We hope this will be a pivotal moment for us," Real captain Iker Casillas told reporters, when he surprisingly appeared to speak instead of coach Jose Mourinho.
"We are level at 1-1 (with United) and we have to try and score, and to keep a clean sheet. We need to do what we did here at Old Trafford," added Casillas, who is out of action recovering from hand surgery.
"The team played to their strengths very well. I think Madrid have beaten Barca tactically and are deserved winners of the tie."
Madrid let Barca dominate possession but denied them the space to work their magic, as AC Milan had done when surprising the visitors 2-0 in their Champions League last 16 first leg last week.
Ronaldo outshone World Player of the Year Lionel Messi, scoring in a record sixth consecutive clasico away from home, the first goal coming from the penalty spot and the second after a trademark fast counter-attack.
The Portugal forward, a former United player who was applauded by visiting fans at the Bernabeu where he headed Real level two weeks ago, hailed the result for it's morale-boosting effect.
"We want to continue in the same vein," he told Spanish television. "This game gives us enormous confidence for the trip to Manchester."
Real are seeking a 10th European Cup, and Mourinho a third with different clubs, and he has made it clear the domestic trophy and the Champions League are his priorities this season with the defence of their league title all but over.