Cristiano Ronaldo scored twice as Real Madrid overcame Barcelona 3-1 at Camp Nou and 4-2 on aggregate to book their place in the Copa del Rey final.
With Manchester United manager Sir Alex Ferguson watching from the stands ahead of Tuesday's UEFA Champions League last-16 second leg with Real at Old Trafford, Jose Mourinho's men produced a devastating display of containment and counter-attacking football.
Barcelona may hold a 16-point lead over their bitter rivals in La Liga going into Saturday's El Clasico encounter, but the Catalan club were firmly second best in front of their own supporters when, as in their Champions League defeat to Milan, they dominated possession but created precious few chances.
Lionel Messi was inches away from opening the scoring with only 90 seconds on the clock as his instant control and shot on the turn from Pedro's cross flashed across Diego Lopez's goal and narrowly wide.
But it was Real who took the lead in the 13th minute when Ronaldo was released by Gonzalo Higuain's clever ball down the wing, with the Portugal ace drawing a foul from Gerard Pique following a series of step-overs.
Pique and Barcelona were infuriated, but referee Undiano Mallenco's decision was absolutely correct, with Ronaldo picking himself up to drill into the bottom corner and send Jose Pinto the wrong way for his sixth successive Clasico goal at Camp Nou.
Fabregas immediately had a penalty appeal of his own turned down at the other end of the field after tumbling under Alvaro Arbeloa's challenge, while Ronaldo fired two long-range efforts over before thudding a third attempt into Pinto's chest.
Parts of Camp Nou thought Barca had equalised with half-time approaching as Messi rippled the outside of the net with a low free-kick from a central position just outside the box after Arbeloa went into the book for bringing down Andres Iniesta.
Xabi Alonso released Fabio Coentrao with a superb ball on the left side of the area but he shot straight at Pinto early in the second half, before Sergio Busquets finally forced Lopez to make a save with a well-struck shot from outside the box.
Real made it 2-0 with another lighting counter-attack which left Barcelona's defence all at sea as a long ball out of defence was chased down by Angel Di Maria, who turned Carles Puyol inside and out to leave the experienced defender on his knees.
Di Maria's resulting shot was superbly saved by the feet of Pinto, but the ball looped up kindly for Ronaldo to control and convert in the 57th minute, with the Real ace receiving yet more unwanted attention from a supporter in the stands with a laser.
Any hopes Barcelona had of mounting an improbable comeback were vanquished when Raphael Varane, who found the net in the 1-1 first leg draw, produced a towering header from a corner with Jordi Alba's late response for Barcelona nothing more than scant consolation.