Jay Emmanuel-Thomas's equaliser denied Birmingham the chance to confirm their Championship play-off place.
Chris Burke gave Chris Hughton's side the lead just before the break with a fine finish from outside the area.
But Emmanuel-Thomas, who had hit the bar earlier, produced a close-range finish late on to earn a point for Paul Jewell's team.
Birmingham are four points above seventh-placed Middlesbrough with two games left.
The hosts dominated the opening period and should have taken the lead when Daryl Murphy lifted his shot well over from just a few yards out.
But Birmingham took the lead before the break when Burke found the bottom corner from just outside the area for his 14th of the season.
After Michael Chopra headed over from a decent opening, substitute Emmanuel-Thomas thumped a shot onto the bar from distance.
But he earned his team a point when he touched in from a Carlos Edwards cross.