The Blues top scorer was used as a second-half substitute despite only having two full training sessions since returning from a knee operation in early December.
"It's good to be back playing and hopefully it's a case of turning the corner with that goal," John told the B'ham Evening Mail.
"When me and Craig Fagan came on for the second-half they scored after about 30 seconds and it killed us.
"We ran around, tried to have a go, and the 45 minutes was a good for my fitness. I've only had a couple of proper training sessions and I'm short of match fitness, but it will come with more games.
"I needed to score even before I had the operation. Maybe it will give me a bit of confidence and the new year will be a better one for me, one in which I can stay injury free."