Barcelona overcame the shock of conceding a goal after just 23 seconds -- the fastest in El Clasico history -- to defeat bitter rivals Real Madrid 3-1 on Saturday and go top of La Liga. (Match in pics)
French striker Karim Benzema scored the early goal to give Real a 1-0 lead after a terrible clearance from Barcelona goalkeeper Victor Valdes.
Alexis Sanchez, who was chosen ahead of David Villa, levelled in the 30th minute after a sublime through ball from Lionel Messi.
A drive from Xavi in the 53rd minute took a wicked deflection off Marcelo and beyond the desperate reach of Iker Casillas in the Real goal as Barcelona went into a 2-1 lead.
Cesc Fabregas then added the third in the 65th minute, scoring with a diving header from a fine cross by Dani Alves.
It was the former Arsenal man's 10th league goal of the campaign.
Real, who now trail Barca on goal difference, still have a game in hand, but this result brought to an end a 15-match winning streak for Jose Mourinho's side.
Defending champions Barcelona are now unbeaten in six visits to Real's Santiago Bernabeu home, but coach Pep Guardiola urged his team not to get carried away.
He is aware that by the time his side return from the World Club Cup in Japan, Real will probably be back on top.
"Real will be the leaders again if they beat Sevilla. There is no point being the 'champions' in November or December."
He added: "I thought it was going to be tougher for us. It was a match in which we were always going to need some luck.
"Madrid were always going to create chances, that has always happened when I have come here, but overall I am happy with the way the game went.
"I don't think that this result will cause distress for Madrid, they will recover and continue to be the biggest rival. Nothing is decided now and it wouldn't be either if we had lost."
Mourinho admitted that the result was disappointing, but that it was not a make-or-break game.
"The players are sad but calm. Before the match we said we had our emotions under control and that this would not change if we went six points ahead or ended up level in the table," he said.
"We have only lost a game and if we win our next match then we are leaders."
For the first time in recent years the pressure was on Barcelona who knew that a defeat would have a serious bearing on the championship race.
Guardiola had been experimenting with a three-man defence but admitted it would be a risk at the Bernabeu with the strength of the Real attack and he chose instead to field a tried and trusted back four which included Carlos Puyol and Gerard Pique.
Mourinho chose to play Benzema ahead of Gonzalo Higuain and the Frenchman put the home side ahead straight after the kick off thanks to some poor defending from Barca.
Valdes gave the ball away to Angel Di Maria and while his cross was cut out, the ball fell to Mesut Ozil whose shot was saved but the rebound fell to Benzema who slotted home.
Messi gave Real reason not to get carried away with a trademark run, going round Sergio Ramos, and seeing his strike parried by Casillas.
The home side should have doubled their lead midway through the half when Ronaldo fired wide inside the box with time to pick his spot.
Sanchez's runs were a constant problem and he drew Barca level with a clinical finish on the edge of the area after a fine pass by Messi.
Barca took the lead after the break through a slice of fortune when a Xavi shot flicked off Marcelo's foot, wrong footing the keeper, and the ball crept into the corner.
Real had the chance to equalise through a Ronaldo header which he failed to keep on target from just 10 yards out, but Barca were also a danger at the other end.
The visitors extended their lead after Alves burst down the wing and crossed to the back post where Fabregas headed home.
Elsewhere, an astonishing injury-time brace from Ruben Castro saw Real Betis come from behind to snatch a 2-1 win over Valencia and end a run of 10 matches without a victory.
Valencia are now seven points behind Barcelona and Real.
A scrambled goal by defender Nano Rivas gave Levante a 1-0 victory over Sevilla which consolidated their fourth place.