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One of the tactical trends of this season has been the unexpected return of 4-4-2.

It was a system that, at the highest level at least, seemed to have been bypassed by evolution as single-central striker systems became the norm. Yet this season, it’s the usual set-up for Manchester City, Paris St-Germain and Atletico Madrid.

All three play it differently—and its flexibility is one of the strengths of 4-4-2—but all have a clear front pairing and a back four; all also play with four midfielders, although it's in how they are distributed that the differences lie.

The main reason 4-4-2 fell out of favour was that it deploys only two men in the middle of midfield. A team playing 4-3-3 or 4-2-3-1 has three men in that zone and so should be able to dominate central areas, which in turn should allow it to dominate the ball—which most teams at the highest level prefer to do.

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Others—and Manchester United did this regularly in the last couple of seasons under Sir Alex Ferguson—accept a deficiency in that area and accept that they will not dominate possession. They choose instead to protect the back four with two deep-lying midfielders, looking to break quickly and use the advantage they should have on the flanks to supply crosses—which, of course, have the advantage of being aimed at two central strikers.

Atletico Madrid operate on that same principle of often allowing the opponent the ball, although for them width is less important.

It’s safe to assume that, even though they’re at home against Barcelona on Saturday, Atletico will look to be reactive rather than proactive: Stats from WhoScored.com show that while Barcelona have averaged 66.4 percent possession this season, the highest figure in La Liga, Atletico have averaged just 48.6 percent, the 10th highest, and a remarkably low figure for a team that has dropped just five points in 18 games and racked up a positive goal difference of 36.

When they won 1-0 away to Real Madrid earlier in the season, for instance, Atletico had only 37 percent of the ball.

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Real played with what was effectively a 4-4-2 that day, so Barcelona may have even more of the ball on Saturday. Unless Gerardo Martino springs a major surprise—and he is a pragmatist who is quite happy to change approach according to the circumstances even if there has been little evidence of that at Barca so far—they will play their usual 4-3-3 with Messi restored as the false nine, placing huge pressure on Atletico’s two holding midfielders, Gabi and Tiago Mendes.

Not only do they risk being overwhelmed by Barca’s midfield three, but they must also guard against Messi coming from behind them, dropping too deep to be pursued by either of the two central defenders, Diego Godin and Miranda.

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Gabi and Tiago are supported in their midfield roles by the fact that the two wide midfielders, Koke and Arda Turan, play very narrow, closing the space in the centre and effectively allowing the opponent to dominate the flanks. Koke makes 2.4 tackles per game and Turan 1.9, unusually high figures for players who are nominally wide midfielders, an indication of just how diligent they are in their defensive work.

Leaving the flanks vacant will encourage Dani Alves and Jordi Alba forward, but Atletico probably regard that as a risk worth taking.

If they can choke the middle, they can allow Barca to swing in crosses from wide given they are likely to dominate any aerial battles. And, if Barca do push both full-backs on, there is the chance of Koke or Turan being able to initiate a break with the strike pairing of Diego Costa and David Villa, both mobile players who can pull wide into the space behind the full-backs, guarded by only two central defenders.

Barca will dominate possession, but who wins will be determined by how well Atletico can clog up central areas and the use they can make of their front two.