And then there were three. Or maybe even four, perhaps, if Pep Guardiola had his way and we counted the Community Shield as a major trophy, as they do in Spain with the Supercopa. Let’s call it three, the first domestic treble by any men’s team in history, and another thumping demonstration of how Manchester City have changed the landscape of English football.

They turned this final into such a cakewalk it was difficult, long before the end, not to sympathise with the latest team to feel the full force of Pep Guardiola’s side. Guardiola had stopped celebrating the goals and, if anything, looked slightly awkward about the ordeal Watford were suffering. The only other time an FA Cup final has been won by this margin goes back to 1903 when Bury put six past Derby. City have played six ties in this season’s competition and scored 26 goals, the most by any team since 1946. And it was the biggest margin of victory in any final at Wembley.

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It was also no surprise, unfortunately for Watford, bearing in mind it was the fifth time in the last 15 months that City have taken possession of a major trophy. Domestically, their superiority is complete, courtesy of two goals from Sterling, another couple from Gabriel Jesus and one apiece for David Silva and Kevin De Bruyne. Though Sterling might be aggrieved not to have finished the day as the first player since Stan Mortensen in 1953 to score a hat-trick in the final. City’s second goal was initially given to him before the FA announced after the game that it was being credited to Jesus instead, by a matter of millimetres.

What cannot be disputed is that it is now a clean sweep for City in terms of the domestic trophies and, whatever slant anyone wants to put on it, that is a spectacular achievement. One that was probably inevitable at some point, 11 years into the Abu Dhabi masterplan, but spectacular, all the same.

Facebook Twitter Pinterest Raheem Sterling puts the ball into the Watford net – although Gabriel Jesus’s shot appeared to have already crossed the line – for Manchester City’s second goal. Photograph: John Sibley/Action Images via Reuters

In the process it was also a demonstration of the gulf that now exists between a team that has just won back-to-back Premier League titles and one that finished 10 places further back, 48 points worse off, playing in only their second final. Watford will not want to be patronised but, boy, it was hard not to pity them, especially during that 26-minute blitz in the second half when they sieved four goals and looked hopelessly out of their depth. City, being City, kept on driving forward, showing little mercy.

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Guardiola did not even subject Watford to a single minute of Sergio Agüero. Why bother when Jesus was playing with such menace? Jesus would have been a worthy recipient of the man-of-the-match award rather than De Bruyne, whose brilliance was restricted to a substitute’s role. Sterling would have been another outstanding candidate but, then again, so would Bernardo Silva, now such a brilliantly influential member of this team. Silva plays as though he would not leave footprints in the snow. But he is a tough little so-and-so. The first goal started from him tussling to get the ball off Abdoulaye Doucouré, pitting the smallest player on the pitch against the tallest. Bernardo came away with the ball and, shortly afterwards, David Silva was swapping headers with Jesus before swivelling to fire in a low shot.

For everyone in Watford’s colours, these were demoralising moments. Particularly, though, their goalkeeper, Heurelho Gomes, on possibly his last appearance for the club. Javi Gracia had decided to stick with the Brazilian because of his involvement in the previous rounds, as appears to be increasingly the etiquette in the cup competitions. Gomes, usually second-choice goalkeeper to Ben Foster, should not be made the scapegoat but he did come for a cross before City’s second goal and missed the ball entirely. As Gomes grasped at thin air, Jesus clipped the ball into the space the goalkeeper had vacated and Sterling followed in to make absolutely sure – which wasn’t difficult given the ball was already crossing the goal-line. Initially, it was awarded to Sterling before the announcement later that he did not warrant the match-ball as a souvenir, after all.

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If anything, City should probably have scored even more in the second half, opening up their opponents time and again. De Bruyne’s goal came from one of those breakaways, running on to Jesus’s pass to step beyond the oncoming Gomes and score with brilliant nonchalance. De Bruyne returned the favour seven minutes later with the through ball for Jesus to run clear and make it 4-0 and Sterling’s goals followed in the 81st and 87th minutes. The first was from Bernardo’s left-sided delivery and the next one, set up by de Bruyne, was also from close range after his first effort had come back off the post.

Facebook Twitter Pinterest Watford captain Troy Deeney looks dejected after Manchester City’s sixth goal. Photograph: Tom Jenkins/The Observer

All of which made it a bittersweet day for those hordes of Watford fans who arrived with their yellow shirts and red flags, like the biggest tub of rhubarb and custard you have ever seen, and might even be bold enough in future years to wonder what might have happened if Roberto Pereyra had taken an early chance to give them the lead and shape, in theory, a very different day indeed.

Would it have made any difference to the outcome? Hypothetical, perhaps, but only 10 minutes had been played and, on the evidence of the next 80, you might assume City would still have found a way to attach their ribbons to the trophy. All that can really be said is that it was a glorious chance. Ederson was quickly off his line to block Pereyra’s shot with his feet. It was a splendid piece of goalkeeping and, after that, there was an air of inevitability about what happened next. City had their treble and the FA Cup had a final like no other in more than 100 years.