This was another afternoon on Wearside to forget for City and one of the players sold by Mancini after winning the Premier League title with them in May was tormentor in chief. Adam Johnson, who moved for £10m in August, had the look of a satisfied man when he walked down the tunnel at the final whistle. After words of praise from old team-mates and City No 2 David Platt there was no such handshake from the man who sold him. Mancini, defeated by the same scoreline by Sunderland on New Year's Day, had already seen enough.
Johnson, albeit with the help of good pal Joe Hart and referee Kevin Friend, was responsible for scoring the decisive goal that leaves Manchester City trailing leaders United by seven points. It doesn't seem too long ago when Johnson curled in a late equaliser for the blues against Sunderland. That was in March 2010, much has happened since. After a slow start to his time back in the North-East due to injury and form, this morning he must feel like his Sunderland career has finally taken off after hitting the net to end Manchester City's proud 11-match unbeaten run away from home.
This was not a performance purely about Johnson, given how Sunderland's resilience was from back to front and caused the opposition's attacking riches a significant degree of problems. After realising Manchester City's defence was there to be broken down, Sunderland ended the first half the stronger of the two and built from there. With James Milner and David Silva effectively playing as an extension to the two man central attack of Sergio Aguero and Carlos Tevez, Sunderland had plenty of blue shirts buzzing around to keep an eye on. And whether it was Yaya Toure making a drive forward from the heart of the midfield or full-back Pablo Zabaleta charging behind Craig Gardner and Johnson, it seemed inevitable there would be an early goal. That never arrived. Despite plenty of nice touches from Manchester City in the opening 20 minutes, goalkeeper Simon Mignolet was more than equal to the clear cut chances which were created in front of him.
Sunderland, relying heavily on the work-rate of both James McClean and Johnson when on the back foot, threatened enough themselves to suggest they are full of confidence after last weekend's victory at Southampton. But it was all about keeping the initial advances from Mancini's team at bay. There were a couple of moments when Sunderland's goal led a charmed life. After Vincent Kompany glanced a header wide from Silva's corner, Mignolet somehow stuck his right boot out to deny Yaya Toure's lowly driven shot from the rebound. Mignolet also had to be alert to charge to his right and pluck a curling 20-yard effort from Yaya Toure from mid-air that was destined for the Belgian's top corner.
And then Sunderland's highly-rated goalkeeper made a superb point-blank stop to deny Silva at the near post when the Spaniard arrived to turn Aguero's cut-back towards goal. While Manchester City's qualities meant Sunderland's penalty area was never quiet, from that moment on Sunderland did have a 35-minute spell when they looked more likely to score. The difference was that Sunderland actually did. Before Johnson's contentious opener the visitors' goal had come under threat on a few occasions. When O'Neill paid £22m out for Johnson and Steven Fletcher in August it was his vision to see the former - and McClean - threatening at pace down the flanks to create space for the two men further forward. It was the performances of Johnson and McClean on the wings which created something yesterday. Even when they were not involved directly the positions they found themselves in created space for team-mates. And when Sessegnon, the smallest player on the pitch, jumped high to nod down a long ball, Fletcher ran in to space and struck a low half volley that had to be turned away by Joe Hart. That sparked Sunderland to life in an attacking sense.
McClean tormented makeshift right-back Kolo Toure with his direct style, while Johnson looked to get involved more in his battle with Zabaleta. Just after half-time it all proved worthwhile. Manchester City started the second half slowly and the blue shirts took an age to react when Zabaleta was grounded by a tackle from Gardner. There was a viable argument that the Argentine had been fouled, but without the whistle or a flag from the officials Johnson picked up possession and attacked Zabaleta's flank. Silva, one of those players to often keep Johnson out of the team at the Etihad, was the man responsible for stopping him, but the Easington-born winger cut inside and struck low towards goal. Hart should never have allowed a hopeful shot to have got under him, but somehow Johnson's effort squirmed beneath and rolled inside the England No 1's near post.
Even after that, despite plenty more attacking intention from Manchester City, Sunderland created the better chances. That, though, was down just as much to some solid defending from the Sunderland defence than anything else. Matt Kilgallon, making only his third Premier League start of the season for the injured John O'Shea, formed a solid last line of defence with stand-in skipper Carlos Cuellar. Full-backs Danny Rose and Gardner never wavered in their support of the centre-backs either. And while Aguero, Tevez, Silva and James Milner struggled to break down the red and white wall, Sunderland should have added to their lead before full-time. Sessegnon had created space for himself and fired wide from a position which deserved better and then the Benin international was denied by the quick-thinking of Hart not too long after.
But there was an even greater chance in the last ten minutes. With Manchester City attacking, Sunderland broke at the other end and McClean was sent clear on goal with just Hart to beat. Rather than hitting the target or aiming across goal, the Irishman's powerful drive went the wrong side of the near post which made for a nervous final few minutes.
There need not have been. Despite the additional four extra minutes, Mignolet's strong arms and Sunderland's dogged and determination on Boxing Day secured a second successive home win for the first time since March.