City were heading for a disappointing draw against their relegation-threatened hosts when substitute Dzeko, who had only been on the pitch three minutes, finished well after the Rovers defence failed to clear a dangerous ball by David Silva in the 75th minute.
It sent City four points clear of fifth-placed Tottenham in the race for the Champions League and increased Blackburn's relegation worries.
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Rovers will feel hard done by but they have now won just three times in 17 league attempts under manager Steve Kean.
This was hardly a vintage City performance but Roberto Mancini's side are now clear favourites to clinch the fourth and final Champions League spot.
They could even overtake fast-fading Arsenal, who currently lie third, after moving to within five points of Arsene Wenger's side with a game in hand.
Since their previous appearance on the Premier League stage, a miserable 3-0 defeat at Liverpool, City have closed in on their first piece of major silverware for 35 years by reaching the FA Cup final.
And Mancini kept faith with the team that overcame neighbours Manchester United in the semi-final as City looked to end a three-match losing run on the road in the league. Blackburn, who started just above the relegation zone, desperately needed a win after taking just four points out of a possible 27.
Yet they almost found themselves behind as early as the third minute when Spanish international Silva let fly with a sweetly-struck left-foot volley which crashed against the post with keeper Paul Robinson beaten.
Robinson was almost embarrassed by Aleksandar Kolarov in the 10th minute, the Serbian full-back's speculative 35-yard effort dipping narrowly wide of the target.
With their 10-season stay in the top-tier in jeopardy, Blackburn, who recalled former City striker Benjani Mwaruwari to the side, needed to seize the initiative.
But despite claims for a penalty after Vincent Kompany's challenge on Jason Roberts, they lacked the cutting edge to seriously trouble City keeper Joe Hart.
His biggest test in a first half of few chances came from David Dunn's 31st minute free-kick which posed few problems for the England keeper.
However, City survived a major 41st minute scare when Blackburn defender Chris Samba outjumped both Kolarov and Gareth Barry to connect with Michel Salgado's cross to power a header just wide.
Whatever Mancini said to his players at half-time appeared to have an impact as the visitors came close to breaking the deadlock inside the opening minute of the second half.
Silva, who was at the heart of his team's best moves, clipped in a cross from the left for Yaya Toure whose header was tipped over the bar by Robinson.
But Blackburn's poor start was a distant memory when Martin Olsson volleyed into the side-netting after Brett Emerton's cross flashed off the head of Jason Roberts into the path of the advancing Swede.
But a game lacking in real quality was settled 15 minutes from time when Dzeko, making his 10th league appearance since joining for 27 million pounds from Wolfsburg in January, let fly from 10-yards after Silva's shot was cleared into his path.
