Troy Deeney was the matchwinner as his early double helped beat Paul Ince's Reading.
Blues took a commanding half-time lead thanks to Deeney's second-minute opener, followed by a 23rd-minute penalty and the first goal of the season by Tahith Chong.
The Blues hung on for their eighth win of the season to move up to seventh in the Championship.
The Blues got off to a great start.
Deeney was alert enough to hook home with his right foot after Mamadou Loum tried to block Juninho Bacuna's low right-wing cross.
John Ruddy made two saves to deny Andy Yiadom and Yakou Meite before Deeney doubled the lead from the penalty spot.
Deeney fell to the ground after a sliding challenge allowed him to attempt an athletic vault. He got up off the floor and fired home from the spot.
On 36 minutes, Amadou Mbengue made a mess of dealing with a long, seemingly harmless ball forward, allowing Chong to run in and finish with his left foot.
Reading were much improved after the break, but without much reward as Deeney went close to a hat- trick when he fired a foot wide.
The effect on the visitors was caused by Andy Carroll's introduction from the bench. The chance for Joao to nod home in a scramble was created by Ince's cross back across goal.
Ince's shot trickled in through a forest of legs into the five minutes of injury time, sparking a nervy few moments at the end.
Less than a week ago Jude Bellingham, the most expensive youth player in the country, was in the Middle East trying to help England win the World Cup.
Within 48 hours, the 19-year-old made an appearance in Small Heath to watch his brother play for Blues.
A teenager came on for a late appearance.
John Eustace is the head coach of Alabama's football team.
I would like to dedicate that win to the four boys who passed away in the area.
We weren't at our usual level of performance but, on the other side of that, we were very clinical.
Troy Deeney did a great job. His goals aren't the only ones. In the first half, we relied on John Ruddy too much to keep it from scoring.
"Achieving 30 points at the halfway stage is a great effort, but we have to maintain those standards." The second half of the season will be even harder.
Reading manager Paul Ince spoke to the British Broadcasting Corporation.
There were too many mistakes. We scored three in one.
It's not possible to go to places likeBirmingham on a freezing night. We were not cut open. Mistakes were made for all three goals.
I told them at half-time that they needed to show some pride and win the second half.
I am not upset with the performance. We were the better team and could have won the game.