Goodness me, that should have been the equaliser. Lionel Messi slips Xavi clean through - Pepe was playing the midfielder onside, and Xavi had all the time in the world to pick his spot. He aims for Iker Casillas' far post, but the goalkeeper is able to get the very faintest of touches to divert the ball inches wide. Weirdly, Real Madrid are awarded a goal kick.
At any rate, that's the second time that Casillas has saved the day for Real Madrid - Barcelona have come close via both Xavi and Dani Alves, but Saint Iker has been equal to both challenges. Messi is going to do his best to ensure that the goalkeeper has plenty more work to do though. He's looking in something of a mood after being shut down against Chelsea.
Madrid are still doing some attacking, of course, but they're snatching at chances rather than building up play. Cristiano Ronaldo has just blazed well wide of goal with a strange long-range attempt, but hey, they're in the lead. They can probably do what they like.
We have live game coverage in our Barcelona vs. Real Madrid, 2012 El Clasico StoryStream. For more on the two teams, head over to Real Madrid blog Managing Madrid and FC Barcelona blog Barca Blaugranes.