The Blues sacked manager Lee Clark earlier this week, and they began life without the coach in terrible fashion, slipping to their biggest ever home defeat having played nearly all of the game with a man less.
Birmingham started disastrously and Bournemouth had the lead inside the first three minutes thanks to Brett Pitman.
The striker danced his way into the Birmingham box before calmly slotting home to give his side an early lead, and it only got worse for the home team minutes later.
They were reduced to 10 men when David Edgar was dismissed for hauling back Callum Wilson on the edge of the box.
Wilson profited from a mistake from goalkeeper Darren Randolph to convert on 36 minutes and double the advantage for the Cherries.
Matt Richie then extended their advantage five minutes before the break with a clever chip.
Marc Pugh inflicted more misery on Birmingham went he headed home the fourth just after the hour mark, before netting in a similar fashion shortly after to make it 5-0.
Tokelo Rantie scored from the penalty spot on 82 minutes before Pugh claimed his hat-trick late on.
There was even time for Rantie to add his second of the afternoon as Bournemouth scored three in the last 10 minutes to complete their biggest ever away win.