In late September 1996, Arsenal travelled to face Borussia Mönchengladbach in the second leg of a Uefa Cup tie. Arsène Wenger had been confirmed as manager but was supposed to have only a watching brief, formally taking over after the following weekend’s match against Sunderland. At half-time, with the score 1-1 and Arsenal trailing 4-3 on aggregate, he came down from the stands to the dugout where, according to the caretaker, Pat Rice, he offered “one or two ideas”.

Arsenal had begun the game with three central defenders (given the wing‑backs were Martin Keown and Nigel Winterburn, it was a back five rather than a back three) but, as Rice explained, Wenger advised him “to go to a back four and add extra width to the attack, and of course I took his advice”. Four minutes after the break, Paul Merson put Arsenal 2-1 up on the night, but as they chased a third they were twice caught on the break and ended up losing 3-2.

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In his programme notes for the Saturday game against Sunderland, which Arsenal won 2-0, Wenger made clear he felt the back three was an anachronism, describing it as “ironic” that “while the rest of Europe are moving to the flat back four, more and more sides in England are adopting the old continental approach using sweepers and wing-backs”.

The lines of his first major debate were drawn. Tony Adams was furious at the newcomer’s meddling in a system in which he felt the team were comfortable. Wenger initially withdrew and Arsenal continued to play with three central defenders for most games that season but by the start of 1997-98 he had his way and the back four had been imposed. Arsenal won the Double and, until the Middlesbrough game a fortnight ago, had played with a back four ever since.

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So why, then, has Wenger, after 20 years, made such a radical change? In part it’s desperation: the defeat at Crystal Palace was so bad something, anything, was needed to shake Arsenal up. It was also an acknowledgement of the fashionability of the 3-4-2-1, an acceptance it is a formation that, in the modern tactical landscape, opponents find hard to counter. The trail Brendan Rodgers first blazed after his toast-fuelled night of the soul has become a major thoroughfare.

The more significant aspect of the shape is probably less the back three than the use of two creators in what are effectively inside-forward positions. They exist in a zone of uncertainty, not obviously the responsibility of the opposition’s holding midfielder(s), full-backs or central defenders, allowing them to exert a far greater influence over the game than one creator operating as a traditional No10.

That was a realisation reached by those who experimented with a Christmas tree (4-3-2-1) in the late 1980s and early-to-mid 90s (Co Adriaanse and Terry Venables perhaps foremost among them, while Carlo Ancelotti wrote his coaching dissertation at the Italian FA’s Coverciano base on the formation). The problem with that system was a lack of width, something attacking full-backs could only rarely make up for. Move the full-backs forward to become wing-backs, though, and cover for that by pushing a midfielder back to become third centre-back and suddenly there is not only width, but a defensive block of five formed by the three central defenders and the two holding midfielders.

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How, then, can the 3-4-2-1 be countered? It’s instructive that eight coaches facing Chelsea this season have opted to match them with a 3-4-2-1. That makes sense: the wing-backs deal with each other, the holding midfielders deal with the inside forwards, a centre-back picks up the centre-forward and there are two spare players at the back to step into midfield, whether offensively or defensively, as required.

When a system is its own negation (as happened with the 3-4-1-2 that took hold in the late 80s following the examples of Argentina and West Germany at the 1986 World Cup), it becomes an evolutionary dead end: the way to stop it is to do the same thing but better.

The 3-4-1-2, as Wenger noted before that Sunderland game, was eventually swept away by a widespread adoption of a back four and a high press, a change of style rather than of shape. But the modern back threes already are pressing. Maybe they will fall, eventually, to a system with three holding midfielders who can overwhelm the inside-forwards, or the narrow back four with wing-backs both Tony Pulis and José Mourinho have deployed at Stamford Bridge this season. Or perhaps somebody will work out an effective way to get behind the wing-backs and so make their advanced position a vulnerability rather than a strength.

For now, though, as Wenger seems to have accepted, the 3-4-2-1 is causing problems that no other shape seems quite equipped to deal with. The danger for him in matching Tottenham shape-for-shape is that it simply exposes Arsenal’s deficiencies. In the vast majority of direct match-ups, the Spurs players look stronger, quicker, more aggressive, better. Tottenham will not be as forgiving as Manchester City were last Sunday. Having made the leap into vogueishness, though, it may be that hesitation is an even greater risk for Wenger.