Surely not again? Ilkay Gündogan had already hit one volley and what a volley it was, inside 13 seconds, the ball flying into the Manchester United net to make him the fastest ever FA Cup final goalscorer.

Now, early in the second half, the Manchester City midfielder set himself again on the edge of the United box, Kevin De Bruyne having pulled back a free-kick into his sphere of influence. United were level at that point thanks to a Bruno Fernandes penalty following a real letter-of-the-law handball decision against Jack Grealish just after the half-hour.

Related: ‘One more to go’: Pep Guardiola urges Manchester City to seal historic treble

Gündogan’s opener had been with his right foot. This time, he allowed the ball to run across him before making the connection with his left and it was certainly not as true. It bounced once, rearing up over Raphaël Varane’s leg, and then again before it reached the corner of the net via David de Gea’s outstretched hand. The United goalkeeper saw it late and was slow to get across.

Gündogan had indeed done it again. City were back in the ascendancy and they were not likely to let it slip, even if United did muster what passed for a late push. Alejandro Garnacho, on as a substitute, was fearless and dangerous, bending one shot inches past the far post while, at the very end, Varane saw a shot saved by Stefan Ortega, who had kept his place as City’s cup goalkeeper. The ball reared up to hit the crossbar before another substitute, Scott McTominay, headed the rebound over.

And so Pep Guardiola and City move one step closer to the treble, the ultimate one – league, FA Cup, Champions League – which only United’s class of 99 have previously achieved. They did it under Sir Alex Ferguson, who was here to watch City advance on the single greatest element of his legacy. That is surely what stings United the most.

It has been a very good season for them – the Carabao Cup won, a Champions League return secured via a third-placed league finish. To have expected more in pre-season would have been too much and whatever happened here would not undo the overall sense of progress under Erik ten Hag.

But the treble matters enormously to United. Its legend is always there, always talked about at the club and to share it with City would not be easy to digest. United will have to hope that Internazionale can beat City in next Saturday’s Champions League final. On this evidence, it will be a slim hope because City are just so convincing in all areas, so powerful. They were the better team here, as they have been all season.

Related: Manchester City 2-1 Manchester United: FA Cup final player ratings

Remember City’s slump in the 1990s? They were fighting to escape from League One when United did the treble. Their journey under the Abu Dhabi United Group has attracted plenty of scrutiny but this is their time on the field, the role reversal with United reinforced some more at Wembley.

Grealish had said a few weeks ago that, at this time of year, Gündogan turns into “prime Zidane”. On the final day of last season’s Premier League, Gündogan had scored twice in the 3-2 comeback win that clinched the title against Aston Villa and he has been decisive on many other occasions. Here was the latest illustration. Surely, he cannot be allowed to leave on a free transfer?

Gündogan had taken the opening kick-off and his next touch was to send a searing volley into the top corner from outside the area. There had been a punt forward from Ortega, a flick on, a clearing header from Victor Lindelöf and then there was Gündogan, moving smoothly onto the dropping ball, to sculpt a masterpiece.

United’s lifeline was a jaw-dropper in many ways. It was unexpected because they had barely entered the final third and also because nobody really saw anything amiss in real time after Aaron Wan-Bissaka headed Fernandes’s diagonal back inside.

City had been pushing, Rodri heading just wide, Erling Haaland flickering. But they got a sinking feeling when Paul Tierney was advised to consult the pitchside monitor. Once there, the referee saw that Wan-Bissaka’s header had gone into Grealish’s hand at point-blank range as the City winger jumped to contest the ball.

It was harsh but Fernandes did not care. The hop, the eyes, the late decision once Ortega had committed to the dive. Fernandes’s knee slide in front of the City support was not a great idea. Lindelöf appeared to be hit by something thrown from the stands as he joined the celebrations.

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It was a contest for the remainder of the first half; City looking a little rattled, Ten Hag’s team starting to play. City shook their heads clear at the interval and, with De Bruyne to the fore, they pushed United back, reasserting their control. City continued to press after Gündogan’s second, De Bruyne twice going close.

What did United have left? A Marcus Rashford blast that flew high and, after Gündogan had been denied a hat-trick by the offside flag, a bit of Garnacho and the last-gasp chance. City are on the verge.