James Chester was also on target as Bruce's side took a 3-0 lead against the club he used to manage and despite Ravel Morrison and Marlon King reducing the deficit, Hull held on to claim the points.
"It was an unbelievable turnaround. But credit to Birmingham, they stuck at their task just when I thought the crowd would turn against them," said Bruce.
"They played their part. Birmingham kept flying the ball into big (Nikola) Zigic and that is the best I've seen him play.
"The team talk at half-time was to keep it tight and they scored again after 12 seconds. It just shows what rubbish you talk.
"But I thought some of our football in the first half was very good. I have some really good players and the way Aluko is playing, is there a better player in the Championship? He has been excellent for us."