Adam Johnson believes Roberto Mancini failed to offer him a fair chance at Manchester City while the Italian feels the England winger lacked the discipline and professionalism demanded at the highest level. There was probably an amalgam of faults and justifiable gripes on both sides but Johnson delighted in jogging Mancini's memory by scoring Sunderland's winner to record an unforeseen setback in City's title defence.

After a deceptively slow start wide on the right Johnson grew into the game and eventually served up a reminder why Martin O'Neill was so keen to spend £10m on him last summer. "Adam's starting to show the form we know he's capable of," said the Sunderland manager. "He was magnificent."

O'Neill has endured weeks of under-achievement from Johnson and several of his team-mates but three wins in their last four games have dragged Sunderland clear of the relegation zone and the Northern Irishman can only hope that beating City will represent a turning point in his Wearside tenure. The slight concern is that a couple of false dawns during an otherwise disappointing 2012 came with a New Year win here against City and a spring-time draw at the Etihad.

Mancini is a superstitious manager and, as the half-time whistle blew, the way he dug his hands deep in his coat pockets, muttered to himself and shook his head seemed indicative of a man fearing a jinx. Monopolising possession, City had dictated the first 45 minutes but, despite the excellence of Carlos Tevez's movement and distribution, Simon Mignolet had rarely been properly troubled. If Tevez's habit of never wasting possession had seen him conjure a decent chance after supplying Sergio Agüero with a brilliant pass, Mignolet proved more than equal to David Silva's eventual shot following Agüero's lay-off. It proved emblematic of a day when, for the first time this season, City lost despite starting Tevez and Agüero in attacking tandem.

Joe Hart had to work considerably harder to dive smartly and divert Steven Fletcher's low drive away for a corner. Earlier City's goalkeeper had looked relieved when, much to O'Neill's chagrin, the referee decided Matija Nastasic had not fouled Fletcher in the area as the pair challenged for Johnson's cross.

A little over half an hour had passed and, significantly, that cross marked the first occasion that Johnson had got the better of his former City team-mate Pablo Zabaleta. On Sunderland's left James McClean was having rather more luck against Kolo Touré. Reprising last season's dynamic form, the young Irish winger persistently troubled the champions on the break. "James has had a pretty difficult time lately but he was truly terrific today," said O'Neill.

With Danny Rose and Stéphane Sessègnon in similarly threatening mode and Carlos Cuéllar and Matthew Kilgallon presenting an obdurate defensive barrier, Mancini's demeanour became as moody as the Wearside sky. It was all very well City demonstrating a seamless, if temporary, shift from 4-4-2 to 3-5-2 but they struggled to get behind Kilgallon.

Johnson had needed a late fitness test on a dead leg before finding his name on the team-sheet but there appeared little wrong with him as he cut inside Silva and, from a right-sided position some 25 yards out better suited to crossing, beat Hart with a shot that squeezed inside his near post.

If England's goalkeeper was annoyed to see the ball squirm beneath his body, Johnson did not initially realise his shot had gone in and had placed his hands on his heads in a shoulder-shrugging "if only" gesture before his team-mates raced over to congratulate him. "Adam did look a bit stunned," said O'Neill. "But I have to admit it was a few seconds until I realised he'd scored."

City's bench vented their displeasure at officials who had allowed play to continue despite Zabaleta remaining down on the pitch after a challenge from Craig Gardner.

Unperturbed, Sunderland might have scored again had Sessègnon not shot narrowly wide but they had Rose, excellent at left-back, to thank for several superlative defensive interceptions, most notably to dispossess the advancing Yaya Touré.

As darkness fell, Rose was far from the only Sunderland player to put his body on the line for the Wearside cause but the roar that greeted the final whistle spoke not merely of relief but of renewed belief in O'Neill's team.