City had been a man down since the 23rd minute following James Milner’s controversial sending off and then went behind to a fortuitous Shane Long goal on 67 minutes.
But City were far from finished and deservedly fought their way back with Dzeko scoring just a minute after he came on as a 79th-minute sub with a superb glancing header and the brilliant Bosnian secured all three points with a breakaway goal after fine work by fellow substitute Sergio Aguero.
The Blues, unbeaten so far this season in the League, were up against a rejuvinated West Brom side who knew a victory would take them two points above the Premier League champions.
After last season’s hard-fought 0-0 draw in this fixture, City knew this was going to be an equally tough afternoon against Steve Clarke’s men.
After bossing the opening exchanges and pinning the hosts back for the majority of the first 23 minutes, the advantage seemed to shift in West Brom’s favour when Milner brought Shane Long down on the edge of the box and was immediately shown a red card by referee Mark Clattenburg.
It was a decision that could have equally merited a yellow card, but with City reduced to ten men, Albion failed to make the extra body count as the Blues steadily regained control. Mario Balotelli wriggled through three challenges only to see his shot blocked from close range and Carlos Tevez also went close.
Roberto Mancini elected to play Yaya Toure in a more withdrawn role and continue with the personnel on the pitch up until just past the hour-mark when he introduced Aguero for Balotelli.
The plan was working perfectly, but when Shane Long timed his run to perfection to connect with a weak Peter Odemwingie shot, he had the simple task of placing the ball past a stranded Joe Hart from five yards and suddenly the Blues had a mountain to climb.
City, whose industry and commitment had impressed throughout, were, however, far from finished and Dzeko’s 79th-minute arrival turned the game on its head.
Within sixty seconds - just as he did at Fulham earlier in the season - the Bosnian found the net, glancing home Tevez’s inch-perfect free-kick to level the scores to send the travelling army wild with delight.
The Blues then endured some hairy moments as sub Lakaku caused no end of problems, just failing to connect with a Odemwingie cross, seeing a shot cleared off the line by Clichy and then spectacularly sending an over-head kick towards the roof of the net only for Hart to make a superb save.
Hart’s brilliance was rewarded when, within a minute, City were celebrating the winning goal.
Aguero broke down the right and with Dzeko charging forward in support, the Argentinian played a slide-rule pass for the Bosnian to sweep the ball past Ben Foster with a measured drive from 20 yards to give his team all three points.
An incredible end to a super City display - and a thoroughly deserved three points for the defending champions.
