But Dzeko equalised within 60 seconds of entering the action with 20 minutes left and then in injury time snatched the winner with his sixth goal of the season.
City first-team coach Platt said: "If you look at Edin's career for Manchester City, the goals he has scored, he has got a lot of heavy goals, goals that are very important.
"I remember goals at Blackburn the season before last which more or less gave us Champions League qualification.
"You look back at last season as well and he got some vital goals. To win the league, Aguero's goal will always be the one but remember Edin equalised.
"He has been a threat all season and his form has been very good all season."