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Carlos Vela charged toward a mass of team-mates on the sideline, Real Sociedad's bench spilling onto the pitch at the Anoeta almost in disbelief. Behind him was a blur of pink, a ball in the net and a scene of remarkable destruction.

Daniel Carvajal had hands on hips. Pepe walked away in a huff. Sergio Ramos stared at the ground. Marcelo appealed in desperation. Iker Casillas threw his arms in the air. Above them all, the scoreboard read Real Sociedad 4-2 Real Madrid, the season's most startling turnaround complete.

The week before the Basques had lost to Eibar, a newly promoted club with the budget of a greengrocer. In the eight weeks that would follow, they wouldn't win again. Worse still, they would barely score in the whole period, manager Jagoba Arrasate quickly losing his job for overseeing one of the least inspiring teams in the division. And yet, somehow, in some way, they'd put four past Real Madrid. Carlo Ancelotti said he was "sorry."

The Italian went on to add that "something has to change." But did it? In February, Los Blancos were hammered 4-0 by neighbours Atletico Madrid. A month later, they were turned over 4-3 at the Bernabeu by Schalke—a Schalke team that wouldn't win again for almost two months.

Fans waved white handkerchiefs that night. Roy Keane said Madrid looked like a "pub team." Ancelotti said he was "sorry."

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That chaotic loss, and the other two embarrassing ones that had preceded it, became emblematic of what separated Real Madrid from Barcelona last season. Indeed, while many will point to Lionel Messi or Luis Suarez or Neymar or Luis Enrique or some sort of wizardry for the deciding factor, it wasn't any of that—it was the basic art of defending. Both teams scored at will, but only the Catalans prevented opponents doing the same. In fact, Madrid tallied eight more league goals than Barcelona last season, but at the same time conceded almost twice as many. In the notoriously fine margins at the summit of La Liga, the latter is what determines titles.

It is, therefore, the task of new manager Rafa Benitez to rectify that discrepancy, to address an area that remains central to the currently lopsided complexion of the Madrid-Barca rivalry. And for Benitez, the challenge's magnitude is immense; he's fighting history.

Spain's last two title winners in Barcelona and Atletico have conceded 21 and 26 goals across their campaigns, respectively. To find a time when Real Madrid went anywhere near those figures, you have to go back two decades to the 1994-95 season. What's more, Real have only boasted the league's tightest defence once since the turn of the century.

It's this scant regard for one half of the game that has defined the historic power shift that's unfolded in the Primera Division over the last decade or so—no matter what Real's attacking power has been. Barcelona have claimed five of the last seven league titles, an imposing haul made more remarkable by the fact that Madrid outscored them in three of those five successful seasons.

This is Benitez's challenge.

Real Madrid vs. Barcelona Last 7 La Liga Seasons Combined G W D L GF GA PTS Titles Barcelona 266 205 39 22 737 203 654 5 Real Madrid 266 200 30 36 733 270 630 1 Author Calculation

Real's defence, of course, has often been enigmatic, the current one particularly so. It's strong but fragile, dazzling but erratic, star-studded but curiously unreliable. Consider its current components.

In Ramos, Madrid possess a 10-year servant of the club, one of the most highly regarded centre-backs in the land. He's a three-time league champion, a Champions League winner, a World and European champion. As a defender, he has it all: pace, strength, ferocity, courage and sublime skill. He's the hero of La Decima, symbolic of his club's essence or identity, a modern personification of madridismo. Ancelotti compared him with Paolo Maldini.

Often standing alongside him is Pepe or Raphael Varane. The former, like Ramos, has won everything there is to win domestically and remains a prominent figure at international level. Powerful, aggressive and imposing, he can, at his best, be a commanding presence, a dominant centre-back. In 2014-15, he also addressed his disciplinary issues, nullifying his greatest flaw.

Varane, meanwhile, is considered the hottest defensive talent on the continent. At just 22, he's already captained France, becoming the youngest player ever to do so. He's had vocal admirers in Ancelotti, Jose Mourinho, Zinedine Zidane and Didier Deschamps. In his skill set, nothing is missing.

Flanking those men is yet more exquisite talent. Carvajal is the right-back for Spain and Real Madrid, a damn good combo. On the other side, Marcelo was probably the best left-back in La Liga last season. Both men are magnificent on the ball, potent two-way weapons in positions that have evolved to demand that very quality.

Those five, that quintet, are the pre-eminent faces. But there are others behind them, too: Fabio Coentrao, Danilo, Nacho and Alvaro Arbeloa represent very capable back-ups. Thus, this team shouldn't have an issue with defending.

But it does.

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What Real Madrid have is a defensive unit in which the sum of the parts isn't what it should be; there's a strangely large discrepancy between the quality of individuals and the quality of the collective.

It's a situation that's particularly paradoxical when you reflect on some of the recent standout performances from the major faces. At different stages last season, Ramos was unbeatable, Pepe was assured, Varane was a wall, Marcelo was an attacking force and Carvajal was a sprinting, tackling monster. But that's the thing: Despite their individual excellence, you wouldn't say they function in symphony. Together.

For contrast, think of Atletico's almost impenetrable defence of two seasons ago. Los Colchoneros' back four were almost telepathic in their understanding, a remarkable cohesiveness underpinning their strength. They moved up, back and across together, never allowing themselves to become separated as they expanded and contracted their shape, seemingly connected by an invisible bungee cord as they did so. Certainly, the ethos and style expectations are very different at the Vicente Calderon than they are at the Bernabeu, but the comparison is still revealing: Real Madrid's back four isn't anything like that.

It's this, therefore, that Benitez has to change. And the answer doesn't lie in the transfer market; it lies internally.

Think of Real Madrid's defence as a V8 engine. You can give the same basic V8 to two different car companies, but one will fine-tune it better to yield more horsepower from the exact same unit. Essentially, that's Benitez's task: to get more out of what's already there.

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The Madrilenian, based on precedent, should be well-equipped for it. Between 2001 and 2004, his Valencia teams were notoriously stingy and at their peak, his Liverpool outfits were, too. A manager who's obsessive over fine details, Benitez is particularly fussy about positional discipline and systematic balance—the sort of boss who won't be at all satisfied with 7-3 scorelines.

"This team has bags of talent," he said at the conclusion of Madrid's tour of Australia. "We have to take advantage of that and just improve that little bit in defence."

Inevitably, discipline and order have formed large components of Benitez's approach this summer, Marca describing his focus as "defence, defence and more defence." With his holistic mentality toward the game's less glamorous side, the still-polarising coach will undoubtedly see the robustness of his back four as interconnected with the defensive capacity of the whole team.

Whereas his predecessor utilised an attacking, flowing 4-3-3, Benitez with his characteristic 4-2-3-1 setup should provide more cover to a defensive quartet that has often been as stranded and isolated as Chuck Noland. In a holding "two," Toni Kroos will benefit from an extra body alongside him, often in the form of Luka Modric, but sometimes the grittier, scrappier Casemiro, too. At the very least, that should constitute some sort of shield for Ramos and Co.

Then, behind them, there's the goalkeeping issue. Despite the uneasiness or coldness of his exit, Casillas, amid his steady decline, did need to depart. From a purely playing perspective, the right outcome has been reached, even if it was reached in a manner that didn't please anyone.

What's left behind is an intriguing battle between two glovemen. For now, Keylor Navas is the No. 1; behind him is Kiko Casilla. The former, in style, is much like the man he's replacing: fast, agile and a terrific shot-stopper. In contrast, the latter brings with him qualities that have been missing between the posts at the Bernabeu for some time: size, power and immense aerial strength. Put the pair in a blender, and you have a goalkeeping super smoothie.

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Navas is the safer option, the less error-prone man and the longer-serving of the two. Yet, even so, the presence of either might inspire more confidence in the four men in front. Last season, the tentativeness and discomfort of Casillas had sadly grown palpable, Ancelotti's back four hampered by a damaging sense of uncertainty behind them. Thus, the knowledge of the Costa Rican's reflexes might be comforting for Real's defensive quartet. So might the Spaniard's expertise in dealing with crosses and corners.

Still, though, the change in identity between the sticks and the restructuring of the midfield remain peripheral issues to Benitez's primary task: fine-tuning that back four, that V8, to find another level.

Benitez will want to curb the impulsiveness of Ramos, narrowing the distance between his extremes. He'll want a more identifiable connection between the Andalusian and Pepe; to address Varane's gambling tendencies; to add a dash of conservatism to Marcelo; to eek extra positional attentiveness from Carvajal.

These are the internal solutions Benitez must find, the solutions that hold the key to not only his own success at the Bernabeu, but to altering the dynamic of the rivalry with Barcelona that has flipped unfavourably against his boyhood club.

As Benitez has acknowledged, the talent is already there; the components he needs he already has. It's up to him to give them clarity in their purpose, to transform them, collectively, from an enigma to a force.

If he can, Real Madrid can and will win titles. If he can't, the club's underachievement will continue.

Follow @TimDCollins