Blackpool manager Ian Holloway and captain Barry Ferguson were sent off as Birmingham cruised to victory.
Centre-back Curtis Davies headed a dominant City in front in first-half stoppage time before Marlon King raced clear after the break to make it 2-0.
Former Blues player Ferguson was sent off on his return to St Andrew's as he appeared to elbow Guirane N'Daw with Holloway dismissed for his reaction.
Nathan Redmond added a late third from the edge of the penalty area.
Whatever Holloway's anger at Ferguson's dismissal, he could have no complaints about the overall result as his side suffered only their second defeat in 10 games.
Birmingham - the only side unbeaten at home in the Championship - were worthy winners.
And the hosts were on the front foot from the start, although King sent the only chance of the opening stages wide after 12 minutes. The striker was then inches away from connecting with Jean Beausejour's cross.
Blackpool goalkeeper Mark Howard also produced a superb double save to deny first Davies and then Nikola Zigic.
Davies eventually put his team ahead on the brink of half-time as he connected with Chris Burke's corner to send a header past Howard. Burke was again the provider after half-time as King was sent through to double the lead.
The game's flashpoint arrived in the 55th minute with the dismissals of Ferguson and Holloway and from then on it was one-way traffic, Redmond deservedly making it three a minute from the end of normal time.