The Serbian netted a last-gasp point for Blues for the third time this season but his header owed more to a glaring error from Kuszczak, who allowed the ball to slip through his hands.
Steven Caldwell headed the hosts in front after 18 minutes with what was his first league goal in 18 months at the club, but the Seagulls levelled soon after courtesy of Ashley Barnes' sixth of the season and second in as many games.
David Lopez volleyed home in style what looked to be the winner just before half-time only for Zigic to equalise late on, with Blues' sought-after goalkeeper Jack Butland then producing a wonder save to keep out Dean Hammond.
Albion's late setback has seen them drop five points beind the top six although they have moved up one place in the npower Championship table to eighth.
Cash-strapped Blues continue to look increasingly over their shoulder at the relegation places, with just win in their last 10 games. They remain in 20th spot - five points clear of danger.
Those present at a cold St Andrew's watched a tentative start to proceedings although the home faithful were roused after 18 minutes.
Rob Hall's corner from the right was met by an unmarked Caldwell at the back post and he powered home a header past Kuszczak.
Yet the visitors levelled in the 24th minute. Andrea Orlandi broke down the left and cut a ball back for Barnes who fired into the bottom corner from 20 yards.
Chris Burke, who netted the winner a 1-0 triumph for Birmingham in the reverse fixture earlier this season, was thwarted by a fine parried save from Kuszczak just before half-time.
And the stop proved crucial as Brighton claimed the lead in the 43rd minute.
The source was again further good work down the left which resulted in Wayne Bridge sending over a great cross to Lopez, who volleyed goalwards and under the body of Butland.
Zigic was introduced by Lee Clark at the break and the towering striker instantly added a new dimension to the hosts' attack but Kuszczak was not really troubled.
A well worked Brighton move resulted in Orlandi's effort being deflected off target by Callum Reilly just before the hour mark, with Jack Butland on hand to turn away the Spaniard's free-kick soon after.
Burke fired wide from distance with 15 minutes remaining before Zigic looped a header over.
The substitute was then denied by a saving tackle by Seagulls skipper Gordon Greer in the closing stages, before the last-gasp drama secured an unlikely point for the midlands outfit.