The Argentine popped up in the closing stages to settle what was an enthralling encounter, but things turned nasty in the final moments of an absorbing evening
In a match that mirrored Sunday's first-leg in terms of drama and goalmouth incident, Andres Iniesta and Lionel Messi had overcome Cristiano Ronaldo's goal to have the Catalans leading at the interval. Karim Benzema equalized in the closing stages, but Messi added a second, his side's third, to secure yet another trophy for the Pep Guardiola era. Marcelo's late red left a bitter taste in the mouth, however, as players clashed in the dying moments.
Guardiola opted for the same starting line-up that defeated Manchester United in the Champions League final in May, with new signings Alexis Sanchez, and most notably Cesc Fabregas, on the bench. For Madrid, its one change from Sunday evening was Fabio Coentrao's inclusion at left-back, with Marcelo omitted.
Barcelona grabbed the advantage on 14 minutes, courtesy of a sumptuous goal from Andres Iniesta. Messi delayed his through pass perfectly, and Iniesta timed his run, before nonchalant scooping the ball over Iker Casillas and into the net.
But the lead was short-lived, as Madrid equalized just six minutes later. From a deep corner, Karim Benzema's bouncing volley was deflected into the net from close range by Cristiano Ronaldo, who sent a hopeful glance in the direction of the assistant referee before celebrating.
Both sides then exchanged chances, as midnight approached in the Catalan city. Pedro produced a superb curling short that Casillas did wonderfully well to palm to safety, then Ronaldo's piledriver was pushed onto the crossbar from Valdes, the effort proving too hot for the shot-stopper to handle.
But Messi, just as he had did on Sunday, struck on the stroke of halftime to send his side in 2-1 up. Latching onto a backheel from Gerard Pique, he held off Ronaldo and flicked his shot into Casillas' far corner.
After the break, the match lost some of its intensity, and the aggression was ramped up, particularly as the visitors attempted to fight back into the contest. Messi and Busquets both came close for the home side, but as Barcelona looked close to seeing out the match, Real Madrid drew level.
On 80 minutes, a corner from the left prompted a scramble inside the six-yard box; Pepe rose highest, powered a ball across the six yard area, and Benzema controlled, swivelled, and slotted the ball out of the reach of Valdes.
Extra-time beckoned. In a bizarre moment, Madrid celebrated the equalizer, but Barca fans embraced the first appearance of Fabregas, who was introduced into the fray.
But Barcelona was not to be denied. With just three minutes remaining, and both sides fighting for a winning goal, the indefatigable Messi collected the ball, played out wide and continued his run to meet Adriano's cross with a sublime volley into the corner to spark rapturous scenes in the stadium.
After such an exciting tie, however, the fixture exploded in injury time. Marcelo wrapped his legs around Fabregas in a wild lunge, to be granted a straight red from the referee. All 22 players descended on the incident, and the officials fought to regain control amidst a flurry of confusion. Mesut Ozil was sent off for Madrid amidst the scuffle.
Once the dust settled, Barcelona could finally collect its title deep into the night, to conclude what was a quite astonishing Clasico encounter.