Gedo also struck twice while Robert Koren found the target once for the home side as they moved above Watford and into second place in the npower Championship.
Birmingham scored late consolations through Peter Lovenkrands and Chris Burke, but it was Boyd who stood out and Bruce was not about to hold back on his assessment of the forward's performance.
"If there has been a better home debut, I haven't seen one for a long time. He was terrific from first to the last," Bruce said.
"He's a good player. You can talk about tactics, formations and systems but this kid oozes ability.
"He can play with anybody. He's a clever footballer. He's made the difference at an important time."
Hull needed to get back to form after a humbling 4-1 loss at Bolton when they conceded three goals in the opening eight minutes.
"The one thing you want is a response when you get beaten in the manner we did last week," Bruce said. "Last week was a bit of a fluke, we had a good response and scored some good goals.
"Birmingham made a couple of mistakes early on and I keep repeating myself, it's about who makes the least mistakes."