What was it that Arrigo Sacchi said about Zlaten Ibrahimovic being strong against the weak and weak against the strong? The big Swede climbed off the bench five minutes into the second half to settle the most expensive match in football history with a sublime volley into the roof of Iker Casillas' net.
In truth, despite his brilliant second-half strike, Ibrahimovic was not the real hero. Much has been said of Barcelona's class in attack over the last year but the energy and resilience of their defence are also the stuff of champions.
Ronaldo was dangerous on his return to Madrid's first team but Gerard Pique was his match. Dani Alves sprung back and forth from defence to attack and played the pass for the goal. Carles Puyol spent 80 minutes throwing himself in front of Madrid's goal-bound shots.
And when Sergi Busquet's sending-off left Barça with 10 men, each of those three defensive heroes put in double shifts to see the home team over the finish line.
The expected one and two for European Footballer of the year to be announced tomorrow – Lionel Messi and Ronaldo – were both passed fit to start but Ibrahimovic again had to settle for a place on the bench leaving Thierry Henry to keep his place in Barca's forward line.
Ronaldo gave Barça immediate problems. With one stepover and a turn of pace, he went past Puyol down the Barcelona right and crossed for Marcelo. The pass was just behind the Brazilian and he leant back and blazed over wastefully. Messi soon responded for Barca. He slalomed through the heart of Real Madrid's midfield before releasing Henry to his left but the Frenchman's shot was smothered by Casillas.
Kaka then glided inside Puyol and laid what should have been goal No 1 on a plate for Ronaldo, only to see the Portuguese shoot straight at Valdes. Kaka could then have scored himself from a Ronaldo assist but Valdes sprinted off his line and into a goal-saving sliding tackle just outside of his penalty area.
Madrid were playing like the home side now, squeezing the midfield, pressuring high up the pitch and looking for the space behind frequently out-of-position Alves. Kaka did exactly that on the half-hour with a ball to Marcelo but somehow as he shaped to shoot Puyol got across to block.
Raul Albiol picked up the first yellow card for pulling back Messi and Abidal robbed Ronaldo only for Keita to over-hit his pass to Henry. Barça were improving and Busquets played in Xavi whose pass sent Henry down the left to win a corner. Casillas was forced to keep out a shot from Andres Iniesta after he connected with Xavi's through-ball.
Barça then wall-passed their way from left-back to left wing but Henry was penalised incorrectly as he tangled with Pepe and Real Madrid were off the hook. The early Real pressure had subsided and Ronaldo was looking like a player who had spent the last 60 days recovering from an ankle injury. But as a team Madrid were still bullying Barcelona in midfield and Xabi Alonso was lucky not to be booked for a late challenge on Busquets.
Barça played keep-ball as the second half started and a frustrated Lassana Diarra was booked for tugging at Messi's shirt. The resulting free-kick was wasted by Busquets who was then booked for a body check on Ronaldo.
Six minutes into the second half Guardiola sent on Ibrahimovic in place of Henry and the change alone was enough to lift the Barcelona fans and the players, with Xavi forcing an immediate corner. But from the kick Madrid broke and Ronaldo was sent through, and looked dangerous, only for Puyol to make his second goal-saving challenge of the game.
Ronaldo again threatened but he was stopped by a superb challenge from Gerard Pique and from it came the Barça goal. The former Manchester Unied defender came striding out from the back. The ball was played wide to Alves and his floated cross hung in the air for Ibrahimovic. The Swede had timed his run perfectly and he connected with an unstoppable volley that Casillas never saw. The Nou Camp clock showed 56 minutes – Guardiola's change had worked but soon he needed to make another.
Busquets was sent off for his second yellow card after stopping a pass to Marcelo with his hand and Barça had 28 minutes to defend with 10 men. Yaya Touré came on for Seydou Keita and Madrid brought Karim Benzema on for a tired Ronaldo but it was Barça who came closest to scoring next with a towering Pique header going just wide. Even with a man less, Barça were playing with time and finding space and Abidal started and finished a move that ended with his shot going just wide of Casillas' far post.
When Madrid did break, Barcelona bodies flung themselves in front of the ball. But Kaka remained a threat. Abidal blocked the Brazilian's shot and from the same player's corner Ramos headed just wide, then Benzema hooked over from the edge of the six-yard box.
Diarra then picked up his second yellow for bringing down Messi and with 10 against 10 the Nou Camp breathed a sigh of relief.
Barcelona (4-3-3): Valdes; Alves, Pique, Puyol, Abidal; Xavi, Busquets, Keita (Touré 65); Messi, Henry (Ibrahimovic 51), Iniesta.
Real Madrid (4-3-1-2): Casillas; Ramos, Albiol (Raul 73), Arbeloa, Lassana; Diarra Xabi Alonso, Marcelo; Kaka; Ronaldo (Benzema 65); Higuain.
Referee: A Mallenco.
Sent off: Busquets 62; Diarra 89.