HUDDERSFIELD's record signing Steve Mounie helped Town book their place in Monday night's fifth round draw though his goal was not enough to take them through.
The £11.5m striker from Montpellier headed home in the first half but Lukas Jutkiewicz capitalised on sloppy defensive play from Town to equalise soon after the interval to earn a replay.
League matters obviously took priority for both clubs. They both made seven changes from their starting line-ups the previous week as Town looked to entertaining Liverpool in the Premier League on Tuesday when Birmingham have a Championship relegation encounter at home to Sunderland.
Mounie was Town's lone striker and, as in the previous round at Bolton, Terence Kongolo and Michael Hefele were partnered in the centre of defence.
After a quiet start Mounie got across his marker and headed down and home after right-back Florent Hadergjonaj had taken a return pass from Collin Quaner and crossed to the near post.
Quaner's drive also brought a smart save from David Stockdale before Town lost Danny Williams to a lower back problem after taking a knock from Cheikh N'Doye, Philip Billing taking his place.
Jonathan Grounds replaced Harlee Dean for Birmingham at the start of the second half.
Jutkiewicz drove beyond Joel Coleman from the edge of the area after first blocking an attempted clearance from Hefele in the 54th minute, following an error from the Town goalkeeper seconds earlier.
Billing went close as Town upped the pace but Jota found space at the other end and fired narrowly wide as the game opened up.
Jutkiewicz also headed over Coleman into the net but was clearly offside and Stockdale raced out to block from substitute Joe Lolley.
Abel Sabiri hit wide after being teed up by Lolley but Jutkiewicz brought the best out of Coleman at the other end.
Lolley should have won it in stoppage time but hit over from 10 yards.
David Wagner admitted Huddersfield paid the price for too many individual errors.
“It isn’t the result which we wanted to have and I think it isn’t the result we deserved,” said Wagner.
“We missed out clear-cut chances, which we had a few of and we made two individual mistakes before we conceded the first goal as well.
“This means too many mistakes in the offence and too many mistakes in the defence and then it’s difficult to win.”
Huddersfield substitute Joe Lolley spurned a golden chance to snatch victory in stoppage time when he blazed Collin Quaner’s cutback over the crossbar.
“We only have a draw, a rematch, nothing that we wanted to have, but now we have it, we accept it,” said Wagner.
Wagner confirmed both Kongolo and midfielder Danny Williams are doubtful for Liverpool’s visit on Tuesday after sustaining minor injuries.