The 19-year-old Serbian has pushed himself into City's starting line up with a string of impressive displays, and is the undoubted highlight of an odd summer's business from Mancini.
Manchester City's transfer dealings this summer will have confused many, with a prolonged period of inactivity suddenly bursting into life with a flurry of deadline day moves, the highest profile of which being the £16 million swoop for Javi Garcia.
In amongst the madness of transfer deadline day, there was one move that very few fans could claim to have expected, as a young defender was brought in from Fiorentina at the cost of £12 million plus Stefan Savic.
The association with Savic may have contributed to the element of doubt around Nastasic at the start of his Manchester City career. Savic had a fairly hapless City career, often making errors in the few matches he was played in. Nastasic is also a young defender from a former Yugoslavian country, but that is where the similarities between him and Savic end.
Belying the idea that Savic needed time to settle into the side due to his youth, Nastasic - who is two years younger than Savic - has come in and wrested the starting spot next to Kompany away from Joleon Lescott.
His first start came away at Real Madrid in City's first outing in this year's Champions League, and although that night ended in defeat, by the time the reverse fixture came around recently Nastasic was well set in the side.
The Serbian has made six starts for City in the league, in that time they have kept four clean sheets and conceded only twice. Nastasic looks comfortable with both the physical rigours of the English league and the technical demands of playing in Mancini's side.
What has been a problem position for Mancini, a problem exacerbated by his tinkering, looks to have been solved for the moment.
City may not have had their best transfer window in the summer, but they did pick out a real gem in Nastasic. Not only is the Serbian the best player they signed, he could end up being one of the best signings in the Premiership this season as City's recent defensive strength has been at the core of their upturn in form, and will no doubt be central to their title bid.