Referee Graham Salisbury waved away Marlon Harewood's appeals after the striker had been felled in the box by substitute Jamie McCombe.
Chris Hughton: "For me, it was an absolute certain penalty. There are some penalties where you are not sure whether the referee is going to give it or not.
"I could have almost looked away because my first impression was just waiting for the referee to point to the spot.
"It was very frustrating, but I couldn't fault the manner, in particular in the second half, of our approach to go and win the game against a good Bristol City side who came with a formation which certainly frustrated us.
"But we had opportunities and if we had taken one of those opportunities, I could have seen us going on and getting further goals."