The system was new, the problems familiar. Having generally used a 4-2-3-1 system this season, José Mourinho started at Watford with more of a 4-3-3. Anthony Martial and Marcus Rashford were deployed on the flanks, while Wayne Rooney, significantly, played a midfield role – which contradicted Mourinho’s pre‑season statement about his intentions for United’s captain. “For me he will be a 9, a 10, a nine-and-a-half but never a 6 or even an 8,” he said in July. At Vicarage Road, however, Rooney was deployed on the right of a midfield trio, a role that would surely have suited Ander Herrera, an unused substitute, much better.

However, Mourinho’s decision to use a 4-3-3 was probably down to the nature of the opposition. Walter Mazzarri is one of the few Premier League coaches to favour a three‑man defence, the system he utilised effectively with Napoli, and Mourinho wanted to use quick wide forwards to push back the opposition wing-backs, turning Watford’s defence into a back five and allowing United to dominate midfield.

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But this plan was undermined by United’s inability to keep possession during the opening 20 minutes and the tables were turned as José Holebas and Daryl Janmaat pushed back Martial and Rashford into their own half. United were essentially using four recognised forwards, but Zlatan Ibrahimovic was often isolated.

Mourinho’s side also had problems in deeper positions. The communication breakdown between David de Gea and Chris Smalling, which presented Odion Ighalo with an open goal he completely missed, demonstrated their nervousness at the back. Marouane Fellaini, forced to adjust his position to anchor the midfield rather than playing as part of a duo, spent much of the first half dropping back between United’s centre-backs to offer extra height, and a spare man against one of the most effective strike partnerships in the league.

But Fellaini vacating his natural zone proved crucial in Watford’s first two goals. For the opener the Belgian found himself in the defensive line, opening up oceans of space for Étienne Capoue, on the edge of the box, who converted Janmaat’s pull-back. It was his fourth goal of the campaign – after none last season. In Mazzarri’s system he is afforded more licence to push forward, whereas under Quique Sánchez Flores he played a very defensive role.

Something similar happened for the second goal. Fellaini followed Roberto Pereyra’s run – which arguably should have been Paul Pogba’s job – and this opened up space for another cut-back, from Pereyra, allowing Juan Zúñiga to blast home with his first touch. Zúñiga, incidentally, had just replaced Capoue.

Watford’s third goal, ironically, saw Fellaini in the right place to cope with a cut-back – but his clumsy challenge on Zúñiga conceded a penalty, which Troy Deeney scored. United were continually exposed in the same zone, albeit in different ways.

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Mourinho had switched to 4-2-3-1 at half-time, pushing Rooney forward in support of Ibrahimovic, with Pogba dropping back closer to Fellaini. Little improved, however, and United desperately lacked a midfielder capable of dictating play from deep. Daley Blind and Michael Carrick were unused substitutes, as was Herrera – naturally more of a box-to-box midfielder, but excellent in a deep playmaking role during Manchester United’s 3-1 victory over Bournemouth on the opening weekend of the season.

This is arguably United’s most damaging defeat so far in a tactical sense. Switching to 4-3-3 seemed likely to get the best from Pogba, but the Frenchman was again quiet and contributed little in terms of playmaking or attacking dynamism. Rooney’s continued presence remains baffling considering his underwhelming performances and after he returned to his traditional No10 position, it was notable the best work in that role came from Ibrahimovic, who dropped deep to orchestrate the move that resulted in Marcus Rashford’s equaliser.

That was the only bright spot in an otherwise desperately poor Manchester United display.