They had to fight back after Nikola Zigic's solitary first half strike set Birmingham on the way to increasing their unbeaten run to 10 games.
But it looked to be another Barnsley hard luck story as they created more goal opportunities only to display their shortcomings in front of goal which keeps them anchored in the bottom three of the Sky Bet Championship.
Fortunately Jacob Mellis scored direct form a 61st-minute free-kick to give them a well merited point.
Despite their impressive unbeaten run this was Birmingham's fifth successive home draw and they have still only won twice at St. Andrew's this season.
If ever a team required a good start it was Barnsley. They produced some promising football and Mellis had a good opportunity but his weak effort was easily mopped up by Darren Randolph.
This highlighted Barnsley's problems which were exacerbated in the 10th minute when Birmingham stormed into the lead.
Callum Reilly, recalled to the side, produced a low cross from near the corner flag and the ball evaded three Barnsley players, including goalkeeper Luke Steele, to enable Zigic to tap home from less than two yards.
Barnsley strived to get back into the game but weak finishing was a problem, demonstrated when Chris O'Grady produced another poor effort which posed no real danger to Randolph.
There was, however, a ray of hope when David Perkins lashed in a powerful 25-yard drive which Randolph had to save at the second attempt.
Showing more attacking skill than the home side, Barnsley continued to create good openings and should have equalised in the 33rd minute when Randolph, not for the first time, failed to gather a shot from Brek Shea.
The ball rebounded to the unmarked Mellis who somehow conspired to screw a close range shot wide of the far post.
It continued to be a catalogue of missed chances for the Tykes.
Stephen Dawson should have scored six minutes before the break when he too produced a weak shot on target after yet more good work by the busy Shea.
Birmingham failed to lift their game as Barnsley continued to push forward only to be thwarted by a goal line clearance by Zigic to prevent Peter Ramage scoring with a header following a corner.
A spirited Barnsley could not be denied indefinitely and the crucial goal came in the 61st minute.
Mellis scored direct from a free-kick as his curling effort easily beat Randolph.