So here we are: the big one. And, for a variety of reasons, this doesn’t just feel like a routine fixture. Without wishing to delve into Sky Sports style hype and bombast, there is genuinely a lot on the line in this Clasico. Win and, given how small the margin for error is in Spain, then Real will take a long stride to the title already. If Barcawin, however, it’s very much open season. Even more so, it could have an effect on the Champions League and any future meetings given how far ahead of the pack these two look.

The big news, however, is that David Villa is dropped for Alexis Sanchez as Barca move to their more routine 4-3-3:

Valdés; Alves, Piqué, Puyol, Abidal; Busquets, Xavi, Iniesta; Cesc, Alexis y Messi

Real Madrid, meanwhile, are starting with Benzema instead of Higuain:

Casillas; Coentrão, Pepe, Ramos, Marcelo; Alonso, Lass; Di María, Özil, Ronaldo; Benzema

Some reading:

Sid Lowe’s required reading for the Guardian: http://www.guardian.co.uk/football/blog/2011/dec/09/jose-mourinho-real-madrid-clasico-barcelona

Here’s my own piece on the intriguing dynamic the whole issue of hunger/motivation creates: http://soccernet.espn.go.com/feature/_/id/994307/delaney:-unquenchable-clasico-thirst?cc=5739

A few interesting dynamics to this match tonight. When both these teams are at their very best, it would be hard to argue that Barcelona are not the better side. As we’ve said many times in the past, no team in history has ever forced opposition teams to play on their terms to such an extent.

But the key question tonight is whether Barca are actually at their best. Real certainly are, having won all of their last 15 games with an aggregate score of 57-9. By contrast, Barca have dropped more points at this stage of the season than at any other time under Pep Guardiola. They’ve had issues with injuries, sharpness, fitness, team shape and – perhaps most importantly – intensity.

But then, out of that, there’s a curious momentum to this game. Real are the form team and also desperate for revenge after that 5-0 and so many Barcelona trophies. But it’s the Catalans who desperately need to win.

The decisive factor tonight could be whether Barca can raise their game to Real’s recent level. And, to be fair, they’ve done it many times in the past: not least int he 2009-10 Champions League group stage when, after a poor run of form and without Leo Messi, they lifted themselves to dismantle Inter and ease themselves into the knock-out stages after it began to look in doubt.

It’s hard to bet against Real on form. But, equally, you’d be a fool to bet against this Barca.

Perhaps best illustrating how Guardiola wants to revert to previous brilliance, he’s switched from this season’s 3-4-3 to their regular 4-3-3 which has routed so many teams – including Real.

Of course, out of all of this, Real only need a draw. But you get the feeling that Mourinho will want to maximise their recent form and really hurt Barca.

By contrast, Barca need the win or else – even at this early stage – the direction of the title is out of their hands. They’ll need favours elsewhere.

One issue: Mourinho has gone for a very attacking team. Is he pushing it too far though? Going toe to toe with Barca tends to be dangerous, regardless of form.

Almost there…

The Bernabeu belting out Real’s portentous anthem “Hala Madrid!”…

We’re off…

GOAL! Real Madrid 1-0 Barcelona

What was Victor Valdes doing!? Barca were spraying the ball about only for the goalkeeper to straight at Di Maria at the edge of the box. His pass eventually finds its way to Benzema who fires home after just 22 seconds.

A lot of errors creeping into Barca’s play already. While Real look ferociously fired up.

And that was the quickest goal in Clasico history.

Brilliant save from Casillas! World-class. Ramos slipped, Messi pounced and pierced the Real defence, forcing a finger-tip save from the keeper.

That goal just goes to show though: the two best teams in the world and we see one of the worst errors you can see on any football pitch.

Game settling into a predictable (but still very entertaining) pattern: Barca pressing and passing in Madrid’s half, Real hoping to hit them very quickly on the break.

Another atrocious pass out from Valdes and, with the keeper off his line, Alonso attempts one of his trademark long-range strikes but it floats to the right of goal

Real pressing relentlessly in Barca’s half at the moment. The question is how long they can keep it up for?

It already looks to have had an effect on Di Maria who, in the process of pressing, slips and appears to pull his groin. Looks like he’s going to have to be subbed off.

Di Maria stays on.

Xavi tests Casillas with a free-kick just at the edge of the box, the ball skimming off the keeper’s fists.

Valdes does not look confident tonight with the ball at his feet.

Oh should have been 2-0 Madrid. Ronaldo shoots wide when he should have scored or indeed passed to Di Maria. Selfish.

It’s very frenzied at the moment. Barca struggling to find sufficient time/space to produce.

GOAL! Real Madrid 1-1 Barcelona

Alexis silences the Bernabeu with a brilliant run and finish. Credit, of course, to Messi for another sublime assist but the Chilean still had a lot to do with two defenders around him. And he completed it superbly, finishing low and hard into the bottom corner from the edge of the box.

You can see the confidence surging through Barca now after that goal. Different team.

Without wishing to get into the same old debate, this game so far has crystallised difference between Messi and Ronaldo.

Ronaldo could have killed game by squaring for Di Maria at 1-0.

Messi forces equaliser by passing for Alexis.

Different situation, of course, but same old story.

Real need half-time at the moment.

Messi very lucky there! The number-10 – who has just been booked – goes in hard on Alonso. The referee goes to take out a yellow only to realise he’d just given one to Messi.

Half-time: and breathe.

Major first-half talking points:

• Real will have to score early in the first because, on the evidence of the first, they look a lesser team than Barca once their hugely impressive early pressing inevitably wears off
• In the context of recent officiating in Clasicos, Messi is lucky to be on the pitch after two bookable challenges following his first yellow. But, in the wider context, the referee showed common sense.
• On that, though, no doubt about the winner of the ever-present personal duel so far. Messi has completely driven Barcelona and set up the goal with a sublime pass. Ronaldo has been largely absent but could have killed the game by squaring to Di Maria… only to selfishly shoot.
• Alexis’s superb goal had a massive effect on Barca, as they looked a different – and much better – team after it. Confidence was surging through them after an error-strewn first 20.

And we’re back under way…

Pique hauls down Ronaldo, creating an opportunity from a free for Real… which the Portuguese then blasts straight into the wall.

But, from the scramble, he’ll get another chance…

… Ronaldo hits it into Valdes’s body. Poor and reflective of his performance.

Supreme tackle from Coentrao to prevent a clear chance for Iniesta after a fine interchange from Barca

GOAL! Real Madrid 1-2 Barcelona

Another freak goal as Xavi hits what is an initially clean volley only for it to deflect off Marcelo and agonosingly creep past Casillas!

Another dodgy kick-out from Valdes there but it’s possible that he’s had a laser in his eye for many of them.

Barca leave two men unmarked at the back post there… as exceptional as they are, they don’t have make some elemental errors

Ozil comes off for Kaka

Alexis forces a fine save from Casillas after a divine Messi slide-rule pass. Barca well in control now and Real reduced to aggressive tackles.

And a perfect example there: an atrocious “tackle” from Pepe who leaves the leg in very late as Messi escapes. Booked of course.

Messi fires the free-kick just wide.

What a miss! Alonso puts a free header on a plate for Ronaldo with an exceptional cross… but he atrociously heads it wide.

GOAL! Real Madrid 1-3 Barcelona

And Real – and Ronaldo – pay the ultimate price. A brilliant cross from Alves and a sliding Fabregas shows Ronaldo how to head home.

Ultimately, Ronaldo could have made it 2-0 and 2-2. Instead, within moments, it’s 1-1 and 1-3.

Barca just look relaxed now. This could potentially get embarrassing.

Should have been four for Barca. Another fine cross from Alves, Xavi fluffs it. This is like a training exercise at the moment.

Benzema gives Barca a bit of a fright though by cutting inside and driving it wide.

Keita comes on for Fabregas.

Villa on for Alexis.

Could have been tense there as Kaka forces a save from Valdes, with the ball then bouncing strangely but just wide.

And that should have been 4-1 again for Barca. Iniesta and Messi cut through the Real defence after Pepe plays an atrocious ball to Khedira. Casillas manages to save and Real just about scramble to keep it out.

Iniesta now – slowly – coming off for Pedro.

Barca could have made this even more embarrassing in the last five minutes. They could have at least four in that time. This is very thorough.

Ronaldo fires a free off the wall. Sums up his night.

FULL-TIME: Real Madrid 1-3 Barcelona

Underdogs? Barca radically overturned that. A hugely impressive performance that blows open the Spanish title race again.

We’ll be back shortly with a full analysis.