Swarbrick incorrectly sent off West Brom's Gareth McAuley for a foul by team-mate Craig Dawson on Wilfried Bony in the second minute of what proved a comfortable 3-0 win for City at the Etihad Stadium.
City took full advantage of more than 88 minutes of numerical supremacy, easing to victory with goals from January signing Bony - his first for the club - Fernando and David Silva.
The result was just what City - and under-fire manager Manuel Pellegrini - needed after a harrowing week in which their title defence was ravaged by relegation battlers Burnley and they were dumped out of the Champions League by Barcelona.
But regardless of the outcome, Swarbrick ensured the headlines would be all about him as he incorrectly gave McAuley his marching orders
It was the second apparent case of mistaken identity in the top flight in three weeks and the third in a year, after other incidents involving Sunderland and Arsenal.
Few could deny Swarbrick would have been right to dismiss Dawson after Bony broke clear and was bundled over just outside the box
But confusion followed as Bony attempted to play on and was knocked over again, this time by McAuley in the area.
Swarbrick, however, had already blown for a free-kick outside the box, meaning that Dawson, number 25, and not McAuley, 23, should have been the recipient of any red card.
City did not dwell on the issue and took full advantage of what was a gift.
They had the game all but wrapped up before the interval with Bony capitalising on their dominance to open the scoring after 27 minutes and Fernando doubling the lead after 40.
The only surprise was that it took so long to score
That owed much to brilliant West Brom goalkeeper Boaz Myhill who, playing in place of the injured Ben Foster, saved well from Silva, Jesus Navas and Sergio Aguero.
Frank Lampard, making his first start since January 4, was also wayward with three attempts from good positions.
The opener finally came after a Fernando shot was blocked by Jonas Olsson and spun in the direction of Bony, who hooked the ball down on the turn and lifted into the roof of the net.
Olsson also played an unwitting role in the second goal, getting in Myhill's way after James Morrison fluffed a chance to clear a corner
The ball broke to Fernando and he stabbed home from six yards.
Statistics at half-time indicated 80 per cent possession to City with 24 shots, while West Brom had not mustered a single effort on goal.
The second half began in much the same manner as Myhill twice denied Aguero and kept out another good effort from Silva
The woodwork also twice came to the Baggies' rescue as Aguero rattled a post and Bony struck the crossbar from the rebound.
Substitute Stevan Jovetic also curled an effort just wide before West Brom finally showed some attacking intent to win a corner
Olsson nodded on the resulting cross and Saido Berahino headed against the bar before former City player Joleon Lescott put the rebound over.
But any thoughts West Brom might still be able to breathe life into the game were dispelled 14 minutes from time as Silva diverted home a Jovetic shot after good build-up play.
It completed the most routine of victories but the repercussions of the game could be felt for some time yet
To City's relief after much questioning of their mettle lately, they will have nothing to do with them.
Source : PA
Source: PA