Raphäel Varane. This kid needs to retire in this club, Real Madrid's management would be a failure otherwise. Mourinho trusted him and the 19-year old defender realized he had to stop Lionel Messi and FC Barcelona. He succeeded.
Xabi Alonso's defensive efforts helped him, and it's true that Arbeloa and Essien played a fairly decent game as well, but he had to bare with a subpar performance from Ricardo Carvalho, his partner in the defensive line. He even saved a terrible mistake from the veteran Portuguese when the ball was ready to cross the goal line in what would have been the first goal for Barcelona even before the first half had concluded. It's frankly hard to believe Varane's performance. If this is his true level, he will be the world's greatest defender.
Diego López made his second debut with the team and enjoyed a fairly comfortable game, but he did stop a good shot by Jordi Alba in injury time. That'd have been the 1-2 goal, so Real Madrid must thank López for his save, because now Mourinho's men will stand a chance of playing the Copa del Rey Final with a good match at the Camp Nou with most of the team available.
Neither team had very good chances in the first half other than Varane's save noted above. Cristiano Ronaldo shot a dangerous free-kick in the first minutes but Pinto made a good save. Xavi Hernández hit the crossbar some minutes after that, but Diego López seemed ready to stop the shot.
Karim Benzema never found himself in the game's tempo (which was quite fast, actually). The French player isn't playing as great as last season, but with Higuaín's current situation, he's probably the best option Mourinho has for that spot.
Callejón left the match soon after Barcelona's first goal to leave room for Luka Modric. That moved Özil to the right wing, where he played better than in the center. Callejón lacks the technique and that's a problem for Real Madrid when the team is trying to counterattack, but his tactical effort is something essential for his team whenever Di María is out. In fact, after Callejón left the game, Barcelona could've sentenced the tie in a couple of counterattacks, but Varane and a bad finish by Pedro stopped them from doing so.
With Modric on the pitch, Özil improved quite a bit. Even though he kept losing the ball too many times by trying very difficult passes, he allowed Madrid to switch defense to offense. Higuaín joined the game after Mourinho realized that Benzema wasn't having his night. The bad thing is the Argentinian player played bad also. He did press Barcelona's defense and stole some balls, but that's an addition to a good striker, not his main ability.
Varane's goal came in the 81st minute off a brilliant cross by Özil after a deflection in a previous corner-kick. The kid completed his marvelous performance with a huge goal for Real Madrid, so he will probably remember this game for quite a long time.
It's hard to recap a Clásico without analyzing Ronaldo and Messi's performances, but the truth is that neither one of them made a big impact in the game. Ronaldo couldn't score a goal in what would've been his seventh consecutive scoring Clásico, but he did have a big chance when Real Madrid was losing 0-1. Messi was rightfully ruled offside after he scored a goal in the last minutes of the second half.
Real Madrid will now have to win the tie at the Camp Nou with Ramos, Coentrao and Di María available. Marcelo will also be in better shape and Pepe's recovery should be almost ready when the end of February comes. That's the reason why Real Madrid should keep believing.