© Lynne Cameron / PA Photos
Will Buckley created several chances for the visitors in the opening 45 minutes, but saw two shots head wide.
Brighton made a strong start to the second half, Andrea Orlandi forcing two saves from Steele within 10 minutes of the restart.
However, the Seagulls were level for just five minutes, as Adam El-Abd conceded a penalty by bringing down O'Grady in the box.
Kazenga LuaLua attempted a shot from 20 yards out as Brighton tried to find another equaliser, but Steele managed to get a hand to it.
Barnsley gave away a penalty inside the final 10 minutes when David Perkins fouled Calderon.
Ulloa took the spot kick looking for his second goal of the evening, but Steele guessed which way the Argentinian was going to place his strike and was able to prevent the visitors from levelling again.
The result moves Barnsley out of the relegation zone, while Brighton sit one point off the playoff places.