Given everything in football – tactically speaking – is relative, perhaps nothing can ever truly be dead. Systems and styles of play that have seemed to have outlived their usefulness drift away, fade from consciousness and lie dormant, waiting for the game to forget about them so they can be triumphantly reintroduced. For a long time, playing three at the back seemed finished, but Napoli's victory over Chelsea on Tuesday night was just part of a wider resurgence.

The reasons for the decline of the formation are understandable. Against a two-striker system, two of the three centre-backs act as markers (whether in a rigid way in a man-to-man system, or more flexibly in a zonal system), with a spare man there to mop up loose balls or, in possession, to step forward into midfield. As two-striker systems yielded to single-striker systems, though, rather than two markers and a spare man, teams were left with one marker, a spare man and a redundant man. If the opposing side, whether playing 4-3-3 or 4-2-3-1, could then force the wing-backs deep, it effectively guaranteed itself an extra man in midfield. It's not that one formation is better than the other; it's just that in certain combinations one tactic tends to prevail over the other.

It's not coincidence that the resurgence of three at the back began in Italy. Partly that's to do with cultural inheritance: in the mid-60s, European football split. In the most general terms, the north and west went for a flat back four, a pressing game and an offside trap, while the south and east opted for a libero, man-marking and a spare man. Until Arrigo Saachi turned up and upset the tactics boards of the orthodox like Christ throwing the moneylenders from the temple, that was the way it remained. Sacchi taught Italy the value of pressing and a back four, but the lessons of Gianni Brera (see James Horncastle's piece in The Blizzard issue two) cannot be unlearned in a generation. Italian football feels comfortable with three defensive players in central areas.

Even when sides played with a back four, the desire to pack the centre was clear: the narrow 4-3-1-2 last season was almost a default in Italy. That meant a series of fascinating tactical battles in Serie A as sides sought space in a crowded centre. The problem came in Europe, as opponents simply shifted the ball into the vast unoccupied autostrada of the flanks. That lay behind Gareth Bale's evisceration of the isolated Maicon (he might not have needed that taxi if somebody had only thought to give him a lift and stood in front of him on that touchline, at least slowing Bale down so he didn't approach the full-back at full pelt), behind Tottenham's impressive performance against Milan in the San Siro and behind Schalke 04's ultimate demolition of Internazionale in the quarter-final, when Hans Sarpei and Atsuto Uchida, two generally unexceptional full-backs, were made to look like world-beaters.

Domestically, the narrowness of much of the league meant that those sides who did play with width prospered: not only Napoli and Udinese with their wing-backs, but also, for instance, Cesena, who exceeded expectations by staying up by seven points. The result this season has been a reaction against narrowness, but a typically Italian one. Rather than an influx of wingers, suddenly three at the back has become fashionable again.

On one weekend in January, 11 of the 20 sides in Serie A deployed it. The reasons are psychologically consistent: a 3-4-3 offers width, while still leaving a back three protected by two screening midfielders. Even the front three which, aping the trend of the late 90s, is often broken from the back seven, can effectively arrange itself in the way it would have done in a 4-3-1-2, meaning clubs can shift to that system without the need for a huge influx of personnel.

That said, not all back threes are the same. There's the back three that operates like a back four, pushing high, pressing and trying to play offside – what might be called a bielsista back three after the way Marcelo Bielsa played with Argentina and Chile (although he, confusingly, has reverted to a back four this season with Athletic). That, for instance, was how Genoa played – and Inter failed to play – under Gian Piero Gasperini.

And then there is the less radical version which, understandably, is the one more generally employed, the back three that recalls the one that Alberto Zaccheroni deployed at Udinese and Milan. Napoli are an odd hybrid. They are capable of pressing, of pushing high and at times looking like a Bielsa side, but their default mode is to sit deep with Gökhan Inler and Walter Gargano patrolling in front of the back three, looking to get the ball forward to the hugely gifted front three as quickly as possible.

Against a side that, like Chelsea, played with a lone central striker, the man who would otherwise be redundant becomes effectively an additional spare man, another body to pick up runners from midfield. If the opponent has an extra man in midfield, so be it. Napoli don't particularly care if the opposition dominate possession. The issue is to hold them at arm's length, prevent easy chances and then strike on the break. That's why Napoli's record is comparatively so much better against the top sides than the bottom: in a mini league of the top seven teams in Serie A they would be second, precisely because they want their opponent to take the initiative.

And that, of course, is dreadful news for Chelsea ahead of the second leg. This Napoli are by no means impregnable. They are susceptible at set-plays and even with three centre-backs they looked far from comfortable against a fairly muted Didier Drogba. The deployment of Juan Mata centrally disrupted them, his movement twice in the first half creating channels that first Ramires and then Branislav Ivanovic nearly exploited with runs from deep.

But this Napoli are devastating on the counterattack. In the second half last night, as Ivanovic advanced, pushing Juan Zúñiga, the left-back, deep, contributing to a spell of pressure in which Chelsea had five decent chances in the space of around 15 minutes, Ezequiel Lavezzi sat in the space behind him and waited for the counter. He wasted his first chance, dragging his shot wide, but after Edinson Cavani had capitalised on a David Luiz slip, he added the third goal, Ivanovic unable to get back.

That's the problem Chelsea face at Stamford Bridge in the return leg. They must take the initiative, but they must do so against a team that wants them to do exactly that.