The first half saw Tevez, Aleksandar Kolarov and Johnson produce hopeful and ineffectual pot-shots for City.
James Milner, Mario Balotelli, Jerome Boateng, David Silva, Aleksandar Kolarov are all 24 or younger.
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City regained the lead before the break when Aleksandar Kolarov curled in a stunning free-kick from 25 yards.
Bridge has struggled to displace Argentine Pablo Zabaleta from City's starting line-up and has faced further competition from summer arrival Aleksandar Kolarov.
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By now, City were rampant and only a series of super saves by Myhill stopped Kolarov and Silva adding to their tally.
It was only when Kolarov's equalizer hit the back of the net less than a minute later that he allowed himself to celebrate.
The Argentine had already hit the post from Aleksandar Kolarov's cross when he slotted home from the spot after Steven Reid hauled Kolarov down in the box.
Dzeko was hauled down clumsily by Gardner and Kolarov prowled on the edge of the box before curling the ball deliciously to the right of a bemused and wrong-footed Foster.
Mario Balotelli, the gifted but volatile media magnet of a striker, had to be restrained after arguing with teammate Aleksandar Kolarov about which of them would take a free kick.
Milner - the current Professional Footballers' Association young player of the year - joins Yaya Toure, David Silva, Jerome Boateng, Aleksandar Kolarov and Mario Balotelli in moving to Eastlands this summer.
City could have been further ahead at the break, and would have been but for Baggies keeper Boaz Myhill tipping a Kolarov thunderbolt on to the bar and also denying Silva when he was clean through.
Following a quick free-kick by Kolo Toure, Reid brought down Kolarov in the left-hand corner of the area and, after referee Martin Atkinson pointed to the spot, Tevez made no mistake to roll it into the bottom corner.
With the last kick of the game, Kolarov was just wide with another dangerous free-kick but it was Birmingham who hung on, leaving Mancini to trudge off the pitch knowing his players had missed a huge opportunity to boost their title aspirations.
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