City looked devoid of energy during the opening 45 minutes after their Carling Cup triumph over Aston Villa in midweek and trailed at the interval to a goal from Sebastien Bassong.
But the home side dug deep once again and a second-half goal from top scorer Craig Gardner means they have only been beaten once in front of their own fans since September 2009.
Redknapp said: "At half-time, I couldn't see any other result other than three points for us. We dominated the first half but they brought (Nikola) Zigic on and that's the best I've seen him play.
"It feels like a missed opportunity. I thought we would win here and at half-time I felt sure we would. I said at half-time that there were more goals for us, to keep going forward, but we started dropping deeper.
"Gardner kept making runs forward and eventually got on the end of something. The same happened last year when they got a last-minute equaliser but this is not an easy place to come and Alex (McLeish) gets everything out of them week in and week out."
Source: PA
Source: PA