A week is a long time in football. At the elite end of the game, careers have been made and broken in shorter periods, heroes becoming villains and the destiny of major honours determined with alarming swiftness.

Just a week removed (well, eight days, to be precise) from their dramatic, ecstatic come-from-behind victory over Manchester City at the Etihad, Manchester United were beaten 1-0 at home by West Bromwich Albion, the Premier League's bottom side.

Having just produced their most exhilarating 45 minutes of football in years to overturn a 2-0 half-time deficit against the champions-elect, delaying their bitter rivals' inevitable title confirmation, the Red Devils were abject and out of ideas against relegation-doomed visitors.

There are many faults to be picked in United's performance against West Brom, and it is now José Mourinho's job to learn from the mistakes he and his side made and ensure lower-ranking, deep-sitting teams do not continue to have such an easy time frustrating the 20-time champions as they have at times this term and last.

One glaringly apparent lesson the embarrassing Baggies reverse highlighted was how ineffective the United attack is when both Alexis Sánchez and Juan Mata are fielded in the wide positions.

Although both are fine players able to offer a degree of versatility – and, according to a report by The Telegraph, both considered among Mourinho's circle of trusted charges who will not be considered for sale this summer – they too often attempt to occupy the same spaces.

With Sánchez, a natural right-footer, on the left of the front three and Mata, a left-footer, on the right, both players are naturally inclined to play their position narrowly, favouring moves inside on to their stronger sides.

This, inevitably, leads to a congestion of the central zone. As the above average position map, courtesy of , shows, Sánchez (No.7) and Mata (No.8) were playing virtually on top of each other, with United as a whole desperately lacking width.

What's more, Paul Pogba (No.6), who United's recent switch from 4-2-3-1 to 4-3-3 is designed to suit, is also moving into the same clogged space, creating a log jam which plays right into the hands of opponents whose aim is to defend deep, compact the play and frustrate.

West Brom, under the temporary tutelage of Darren Moore, came with a simple plan: hold a deep line, limit the spaces between defenders and protect the back four with a line of five men on the edge of the defensive third.

From there, when possession was won, they'd look to counter through the pace of Jay Rodriguez, who'd drop in to augment midfield during the defensive phase, and the power of Salomón Rondón.

It was hardly rocket science and it really shouldn't have proved as effective as it was.

One of United's main issues, time and again, was their narrowness, a problem caused primarily by Sánchez and Mata's tendency to drift infield rather than hold a wide berth and stretch the Baggies backline.

As the above graphic shows, Sánchez (circled white) and Mata (blue) were regularly occupying an almost identical lateral zone.

It is a problem exacerbated by the fact United don't play with especially adventurous full-backs; if the wide defenders either side of the two “wingers” were more willing to push high up along the touchline, the West Brom back four would not have been able to defend within the width of their penalty area the way they did.

This, in turn, would have opened up spaces for Sánchez and Mata's central movement to exploit. But that wasn't the case and the former Arsenal and Chelsea stars served only to hamper their side's attacking prospects by continually and predictably moving into occupied space.

The same issue is depicted above. Mata and Sánchez are again in close proximity centrally. This time we see left-back Ashley Young (circled green) holding a high, wide position.

This should, in theory, force the West Brom right-back, Allan Nyom, to worry about the space outside of him. However, with Sánchez so far infield, the Baggies are able to have double coverage on Young, and the England left-back, another right-footer, has a natural inclination to shift the ball inside and cross from deep with his stronger foot, rather than breaking in behind and whipping balls in from the byline. The West Brom defenders don't need to pay heed to any danger a more natural left-back would provide.

On the right flank, while Antonio Valencia operates on the side of his stronger foot, the 32-year-old Ecuadorian is not the dynamic threat he once was, now less able to break onto open space and often elects to hold a position behind United's attacking progress in fear of a turnover.

This time we see Sánchez holding a wide position. The Chilean is unmarked as West Brom continue to defend narrowly inside their own penalty area.

Although Mata is again central, United should be able to expose the space outside and in behind Nyom by working the ball quickly to their No.7 and utilising their two-v-one scenario to get Sánchez in behind the defence.

However, once again, as soon as he receives the ball, Sánchez immediately seeks to move inside, and the lack of an overlapping full-back, who would be expected to make the run indicated by the red arrow, renders United's attack predictable and eminently defendable.

Going forward, Mourinho must decide which of Mata and Sánchez he feels should start each game and field one of the creative attackers in conjunction with the likes of Marcus Rashford, Anthony Martial or Jesse Lingard, who can all offer a greater threat in behind, more pace and a willingness to hold a wide position and give variance to an otherwise one-trick attack.

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