This, of course, is why they waited for him, why they courted him, why they put everything in place to make it just right.

This is the momentous occasion Manchester City's hierarchy hoped Pep Guardiola would provide.

Well, it is the starting point at least. It is one thing beating Barcelona in the group stage, quite another to do so in the knockout rounds.

But until Tuesday night, City had not defeated Barcelona in this competition at all.

Sixth time lucky, except luck had nothing to do with it. City deserved this. They outplayed Barcelona. Over 90 minutes, they were far the better team.

It could have been more. City had a worthy penalty appeal turned down and missed a greater number of chances than they converted.

Guardiola's high press put a fragile Barcelona back line under duress, and the margin did not flatter the winners.

Yes, Barcelona are weakened at the back right now, but that should take nothing away from City.

To recover from a 4-0 humbling in the Nou Camp takes grit and faith — and they fell behind here, too.

For the period that followed Lionel Messi's 21st-minute goal, his 16th in 14 matches against English sides in Europe, the visitors looked untouchable.

It would have been easy for City to crumble. They didn't.

They got a foothold in the game and dominated from there.

After Ilkay Gundogan's 39th-minute equaliser, there was only going to be one winner.

Gundogan's performance was a triumph for Guardiola, too.

His summer signing scored twice and dominated midfield in the way Yaya Toure used to, except Toure never did it against Barcelona.

And while City's defensive frailties remain, after last season's semi-final appearance this was a performance that suggests the club could be genuine contenders for the European title this season.

Just as Guardiola's employers hoped.

The third goal encapsulated City's supremacy.

Kevin De Bruyne put a beautiful pass behind Barcelona's back four, Jesus Navas crossed and when Sergio Aguero could not get the required contact, the ball fell kindly for Gundogan to strike home.

Barcelona had been opened up, as City were at the Nou Camp last month.

Guardiola must have been pleased because, for once, the coach allowed himself a brief celebration, a fist pump and a purposeful stride back to his bench.

That's real joy in Guardiola's world. That's Sally Field at the 1985 Oscars stuff.

Guardiola is on a steep learning curve here, though.

He is finally finding out what it is like to fight against European aristocracy, rather than be part of it.

As manager of Barcelona and then Bayern Munich, he was on the side of the angels as far as UEFA were concerned. It is different managing City. It is harder to catch a break.