It came in 2008 as Sheikh Mansour completed a surprise takeover of the previously often hapless Premier League outfit and embarked on an extraordinary spending spree that catapulted them into title contention.
With considerable extra investment in infrastructure, the club was quickly transformed not only on the field but off it too, building a base that would enable them to sustain prolonged challenges for the biggest prizes.
Former City defender Onuoha, a graduate of the club's academy, was there at the start and, as a lifelong fan, has followed closely all the developments since.
"When that takeover happened all of a sudden the ceiling went to a whole new height," Onuoha, 34, told the PA news agency.
"It was exciting and, although as a player you're not sure how it affects you, you could see that from the get-go.
"On day one we got Robinho. That's not someone that would ever have come beforehand.
"When someone like that arrives, and it's not just an isolated incident and you start to see more players of that calibre coming to represent City, and they are making changes to the training ground, making changes to the stadium and surrounding areas, and looking to build a new training ground, you can't help but realise it was very different.
"What was happening was special and it seemed like it was a long-term commitment, they were building an infrastructure.
"And they've built it so well to the point now where, in my opinion, seeing them in the Champions League final doesn't seem like a surprise."
One of the great joys for City fans along the way has been how they have eclipsed neighbours Manchester United, in whose shadow they had grown used to living throughout the previous two decades.
They even went about it an brazen way, signing one of United's star players in Carlos Tevez in 2009 and putting his face on a billboard above the words 'Welcome to Manchester'.
"For the first two years you could see the land shift because they kept talking about City," said Onuoha, who joined QPR in 2012 after a loan spell at Sunderland.
"The Tevez thing didn't go down well, City beating United in the FA Cup didn't go down well. Then City got better and better and better.
"Most people would now say City are the better team and that's not something I thought I'd see in my lifetime."
The challenge for City is now to fulfil their ambitions and claim the Champions League crown but, such is the club's strong base, they will hope Saturday's final is no one-off.
Onuoha said: "For City to be starting this season as one of the favourites for the Champions League shows how far they have come and that they are part of that conversation signifies success.
"It isn't a case of they hope they can do well in the Champions League each year, the expectation is they will do well, and that comes through everything that they've done."