The amount of money Manchester United have spent and will spend on Di María is extraordinary but then so is he • Barney Ronay: Mourinho got a total education under Van Gaal

Football was invented for a single purpose – to make people happy – and accordingly football clubs exist for a single purpose – to make their supporters happy. So it is often curious when a football club is accused of overpaying for a football player since, unless the funds would otherwise subsidise admission, they can have no better use.

It is unlikely that this was the intention of the Glazer family, had Angel di María not moved to Manchester United – and yet, the expenditure that secured his signature attracted plenty of criticism. Clearly £59.7m in fees and £280,000 a week in wages is extraordinary but then so too is Di María; players of his quality and qualities are cheap at whatever exorbitant price you are lucky enough to pay for them.

Paradoxically this is an approach not of extravagance but of prudence. An indisputable star is far more likely to succeed than three cheaper players bought with the same money. Prior to this summer United had broken the British transfer record six times – expensive acquisitions are as much part of the club’s tradition as developing local talent – and in return, received Denis Law, Bryan Robson, Roy Keane, Andy Cole, Juan Sebastián Verón and Rio Ferdinand. With the exception of Verón each was an enormous success.

Véron may have been better than he is given credit for but, while he was languid, Di María is rapid and, where his arrival compromised a midfield, Di María has redeemed one.

Even so there were plenty who argued that United’s principal needs were elsewhere, particularly after the loan of Radamel Falcao. After their collapse at Leicester Ruud Gullit commented that “you start with the foundation and you build the roof of your house last” – a glib line and not obviously cognisant of the differences between domiciles and football teams.

Nor is it an entirely accurate representation of what happened. Louis van Gaal also signed Marcos Rojo, Luke Shaw, Daley Blind and Ander Herrera, men who either defend or protect the defence. And, when preferred targets become available, there will be further additions. Since the window closed, there is plenty for which Van Gaal might be criticised but his work during it showed a man aware of his problems.

And he inherited a team with attacking issues, scoring a mere 64 times in the league last season and only once against its top three sides – a set piece, in the 87th minute, of a 4-1 defeat. Then, at the start of Van Gaal’s tenure two apparently easy fixtures yielded plenty of possession but only two goals and very little zest – or, put another way, United were as desperate for Di María as a team lacking pace, tempo, imagination and conviction is desperate for pace, tempo, imagination and conviction.

His influence was immediate. The urgency and economy of his passing evoke Roy Keane, which, combined with the ability to beat men at extreme pace, to cross superbly and to shoot accurately from distance, makes him unique in world football. It is true that his goals record is merely acceptable but playing behind Gareth Bale, Karim Benzema and Ronaldo is like arriving at a buffet once Fatty Foulke, Augustus Gloop and Roland Browning have left. For United he has three in six games.

Essentially there is very little that needs doing on a football pitch that Di María does not do very well and with purpose; even his tricks are functional. Deployed only as the best means to a known end, they are neither conceited rumination nor performed for their own sake, rather, like all the most important art, aimed at achieving something specific, specifically when it needs achieving.

The other side of this utilitarianism manifests in his desire to chase around, energy that enables him to fill two roles at once, midfielder and left-winger, engine and spark plug. And this is part of a wider trend that has seen players able to beat men moved from the flanks into central areas – Raheem Sterling, David Silva and Lionel Messi, for example.

Though cover provided by the voguish sitting midfielder allows full-backs to push forward into the vacated space, the rationale is as much sensible as tactical: beat a man out wide and get to put in a cross; beat a man infield and open up the entire pitch. And, even more than that, some players are just too good to be confined to the periphery, as Di María was at West Brom; his involvement in a game must be a given, not at the mercy of flow and service.

Along with Cesc Fàbregas, Di María has been the league’s best player this season but, unlike Fàbregas, his ability to transcend the biggest Premier League games remains expectation rather than fact. With United preparing to face Chelsea and then Manchester City, he has the chance to alter that; they will certainly need him to. But regardless of how he performs, of one thing there is no doubt: a team with Di María in it cannot help but fulfil its existential imperative.