You probably know of Sir Isaac Newton thanks to his famous First Law which, if you discard the mathematical theorem, simply says: “The Clásico will be all about Ronaldo and Messi again.”

But he patented another important physical rule, lesser known, which is that ‘for every action there will be an equal and opposite reaction’.

Isaac was a big football fan, hooked on Revista de la Liga and a regular Paddy Power punter. Had he been around today he’d be telling you to look at the last five years of FC Barcelona’s play to find the proof of his scientific doctrine. Particularly ahead of Saturday’s Clásico.

Under Pep Guardiola Barcelona pushed so hard against errors that, particularly in the biggest games, they practically eliminated them.

Tiki-taka and clusterf***s

Despite playing the most intricate, most difficult, highest-paced technical football we have probably ever seen (and I do mean ever) Guardiola’s Barça consistently chose the right passes, pressed and robbed the ball in the right way, moved off the ball with unrelenting intelligence and alternated between killing off the opponent and killing the tempo of the match with computer-like reliability.

Moreover, particularly in Clásicos, Barcelona displayed a shark-like hunger to wait for and then exploit even the most minor miscalculation or slip in concentration Madrid showed.

The last year of football at the Camp Nou, without Guardiola, has evidenced the equal and opposite reaction pushing right back. And often pushing harder.

From the first Guardiola-free Clasico, which was August 2012, until now there have been six Barça-Real Madrid meetings of which the Catalans have won one.

More importantly for fans of Newton, and those who like a well informed punt, Barcelona have committed a series of catastrophic goal-errors.

Barcelona brain freeze

From the moment in the first post-Guardiola Clasico when Iker Casillas makes an extraordinary save face to face with Xavi, which would have left the home side 4-1 up, it starts.

Madrid chase a ‘lost’ ball all the way up the pitch, Victor Valdés has a brain freeze, Di Maria nips possession off his toes and scores for 3-2. You wouldn’t see it in a primary school playground.

Mascherano and Piqué succumbing to the long ball to concede twice in the return game and Adriano getting himself sent off for a last man challenge – a series of positional errors. They lose 2-1.

In the first Liga Clasico last season, a belter of a match in the event, Dani Alves doesn’t mark Ronaldo, and Valdés is surprised at his near post for Madrid’s first goal. At the second Adriano lumberingly plays Ronaldo onside for 2-2, Barcelona having protected their lead for all of five minutes. Ahead twice, no better than a point.

When Madrid stroll home 3-1 at the Camp Nou last January to win the Copa semi final Piqué dives into a penalty tackle, Puyol falls over in front of Di Maria’s dribble for the second goal and Varane is unmarked for the header which adds salt in the wound.

Then in the second Liga Clasico, when Barcelona play and behave as if they know their goose is cooked, Morata goes completely unchallenged down the left to cross for Benzema who’s unmarked at the back post to score.

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Errors, errors everywhere

Eleven horrible errors which all either allow extremely avoidable goals or bring a red card – in the space of just one year and six Clasicos.

What  they mask is that during considerable periods in the Supercup ties, the first league Clasico and particularly the 1-1 first leg Copa semi final tie, Barça played some top quality, creative, inventive football  which carried threat and seemed to indicate that their collective confidence against Madrid was undamaged without Guardiola.

But their ferocity, their attention to detail and their intensity was.

Piqué explains it best.

“Historically Barcelona has been behind Real Madrid. During the last 10 or 15 years there has emerged an extraordinary generation of players without whom we couldn’t have inverted the situation as we have regularly. We can’t spend what they do. Then there is Pep. The best coach I’ve had, particularly in terms of analyzing an opponent.

“It felt like he’d been watching videos of them for 24 hours every day. Before a match he’d say, ‘look, they play like this, or like that and we’ll have to shift a little to the left or the right in order to blunt them .. and then we’ll attack like this…’. He created a defined identity in how we thought and we played. It was the same away to Granada, away to Malaga or on a pitch covered in puddles. Pep really created this team.”

His absence created a vacuum into which Madrid strode.

But signs that things are changing under Tata

These last few weeks while the Catalan press has been scratching around for things to complain about there have been signs that while Tata Martino is no Guardiola, nor pretends to be, he’s been true to his word in what he wants to restore. Greater concentration, better pressing (albeit less high up the pitch) exploiting the occasional long diagonal pass aimed at Neymar and more regular shooting from distance in order to vary the attack.

He goes into this game with some doubts.

Is it simply because Messi has missed a couple of weeks with a thigh problem that he’s looked subdued during his minutes on the pitch against Osasuna and Milan this week?

Will Piqué, who has played with consistency, good judgement and strength this season, be fit to start having felt hamstring pain on Tuesday in Milan?

Should Pedro or Cesc start up front with Alexis allowed to play as an impact sub when the game is stretched?

And, importantly, what kind of game will referee Undiano Mallenco allow?

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Real Madrid have won all games under this ref

Without a hint of suggesting he might be biassed it remains a fact that Barcelona’s players think he’s allowed Madrid too much freedom to play physically, allowed them to gain an intimidatory edge in the recent Clásicos he’s taken charge of – all of which Madrid have won. (1-0 in the Copa Final of 2011, 1-2 in Guardiola’s final Clásico and 1-3 in the Copa semi-final last season)

In signing Neymar, but nobody else, Barcelona effectively made one of two statements: Either they think that they already ‘own’ the remedy to the embarrassing run of one win in six Clásicos or they think that the Liga, Copa and Champions League can be won irrespective of how they perform against Los Blancos.

Recently they’ve been victims of Madrid’s greater height, power and athleticism plus street-smarts, concentration and cutting edge. Quite a list.

But, despite Madrid both cutting the points gap in the league this week (a win would put them equal top) and registering a third straight Champions League win they do not yet look as error free as they became against Barça in Mourinho’s last 18 months.

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Some ‘dark horse’ betting tips

At the time of writing the sides shape up like this…

• Real Madrid: Diego, Carvajal, Ramos, Varane, Marcelo: Khedira, Illarramendi, Modric: Bale, Ronaldo, Di Maria.
• Barça: Valdés, Alves, Puyol, Bartra/Piqué, Adriano: Xavi, Busquets, Iniesta: Pedro, Messi, Neymar.

Hopefully the football will be glorious. Hopefully the side you back wins.

Some ‘dark-horse’ ideas? Tata Martino asking his side to shoot from distance more often does offer a chance of Busquets or Alves being a high-odds anytime scorer. Bale is by no means sure to start but in his intermittent time on the pitch he’s put shots on target, created a penalty and scored from Dani Carvajal’s cross.

Neymar will start as favourite to garnish his Clásico debut with a goal … but it’s feasible that Bale might end his rather frustrating start to life in La Liga, and making himself a bit of a Madrid legend in the process, by putting one in the Barça net.

To me it looks like another Bishop Desmond game. 2-2.

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