Hart twice kept out former Arsenal striker Gervinho and had Martin Demichelis to thank for two clearances off the line.
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But the goalkeeper also reserved praise for Nasri, whose goal gave City the resolve to hold on to their win and qualify for Monday's knockout draw.
"It's amazing - and what a great effort from the fans," he told Sky Sports. "It's a difficult place to come - a long way on a Wednesday night - but Samir's scored an unbelievable goal.
"We never thought we couldn't do it - we're a strong unit. We had a slow start but we've got character and we've got fantastic players.
"We're moving in the right direction - we've really stepped it up over the past few games."
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