Blues' seven-game unbeaten home run was brought to a disappointing end on Saturday afternoon after they were well-beaten by Barnsley at St. Andrew's.
Both sides had several opportunities, but it Barnsley that made theirs count with Marc Roberts heading home just before half-time and Sam Winnall sealing the victory with two late headers.
Although Blues had chances, their overall performance level was lacking and they couldn't have too many complaints about the result, particularly as they ended the match with ten-men after David Davis was red-carded in the 71st minute.
Gary Rowett elected to go with the same starting XI that had beaten Brentford in their previous league fixture.
However, there were two changes on the substitutes' bench with Stephen Gleeson and Viv Solomon-Otabor coming in for Diego Fabbrini and Jacques Maghoma.
Ahead of kick-off there was an impeccably observed minute's silence in remembrance of the Chapecoense players and all those other passengers that perished in the tragic Colombian air accident.
There was a bright start from both sides, but it was Blues that went close after just three minutes when Barnsley stopper Adam Davies just got to the ball just ahead of Lukas Jutkiewicz with the striker poised to head home from David Davis' cross.
At the other end of the pitch Blues had to be thankful to captain Michael Morrison for putting in a superb block to deny Tom Bradshaw's attempt on goal.
Central defensive partner Ryan Shotton then thwarted the same Barnsley player with a peach of a tackle inside his own box.
Blues should have taken the lead in the 12th minute through Clayton Donaldson. David Cotterill curled in an excellent low cross from the right to the far post, where Donaldson just had the keeper to beat but he was denied by a fine save from Davies who spread himself to block the ball and force it away.
In what was becoming a lively encounter, Barnsley were denied at the other end when Tomasz Kuszczak produced a brilliant diving save to tip Ryan Kent's powerful low drive around the post.
There was no let-up in the action as fine piece of attacking play down the right by Blues saw the ball reach Jutkiewicz just outside the area. The on-loan Burnley man swivelled on the spot before unleashing a low shot just the wrong side of the upright.
Blues continued to press and Davies needed to be alert to save Morrison's header from a corner.
But it was Barnsley that drew first blood in the 38th minute when Roberts got on the end of free-kick from the right and glanced a header home from the middle of the penalty area and into the far corner of the net.
Blues were a whisker away from levelling the scores five minutes later when Davis' low shot cannoned back off Barnsley’s far post and back into play.
Half-time: Blues 0 Barnsley 1
Both sides emerged for the second-half unchanged.
Barnsley made the better start and Kuszczak was forced into some early action when he saved Winnall's shot low down to his left.
The Tykes then won a free-kick in a dangerous position just outside the D, but fortunately for the hosts Winnall curled his effort well over the bar.
Blues were coming under all sorts of pressure and Kuszczak had to be alert to push Bradshaw's goalbound effort around the post.
In an attempt to sway the game back in his side's favour, Rowett made a double substitution just before the hour-mark when he sent on Che Adams and Greg Stewart for Lukas Jutkiewicz and Maikel Kieftenbeld.
Blues were attempting to up the ante, but were struggling to put any decent pieces of passing play together and the game was becoming a scrappy affair.
To compound matters, David Davis was sent-off with 20 minutes to go after collecting a second yellow card of the game for a lunging studs-high challenge on James Bree.
As the game entered its final quarter of an hour, despite Blues pushing forward it was the visitors that were looking the more likely to add to their advantage and they did just that on 84 when Winnall headed home at the near post from a corner.
Then to compound matters, the same Barnsley forward put the game out of sight with second headed goal just three minutes later from a well-placed free-kick.
Blues must now quickly regroup as they get ready to travel up to Championship leaders Newcastle next weekend.