The Blues winger scored the second goal of the game when he latched on to Jermaine Pennant's cross just minutes before half time - his first goal for the club in his 30th appearance since moving to St Andrew's from Crystal Palace in the summer.
"It's been a long time coming," Gray said after the game.
"I've had quite a few opportunities but unfortunately they haven't gone in but luckily today I got on the scoresheet after a great ball from Jermaine Pennant.
"For us to do the double over Liverpool is a great boost for us."