The second 45 minutes was in complete contrast to the first, which Derby dominated and only the reflexes of goalkeeper Michael Kuipers had kept the visitors in the game.
But once Derby lost mid fielder Rob Lee and defender Danny Higginbotham at half time, the game changed and John Gregory's team was left struggling to hang on.
In the end it was the 30th minute penalty expertly put away by Higginbotham that separated the teams, although Brighton clearly felt the spot kick should not have been awarded.
Referee Paul Rejer awarded it for handball against Adam Hinshelwood as the defender stumbled, but Brighton felt it was accidental at worst.
After the protests were waved away the former Man United defender sent Kuipers the wrong way to find the bottom left hand corner, but the Dutch man was not beaten again.
He had already kept out a 25-yard shot from Craig Burley and he made another excellent stop in the 40th minute to deny Warren Barton.
But his best stop came three minutes later when Burley flighted a free kick to the back post and Chris Riggott's down ward header looked certain to find the net only for Kuiper's to scoop the ball behind for a corner.
Brighton had hardly figured as an attacking force but it was different after the interval with Bobby Zamora heading just over in the 57th minute.
The highly rated striker was even closer in the 68th minute when he before driving in a right-foot shot that Lee Grant pushed behind, and there was another great chance for the Seagulls a minute from the end.
Gary Hart made a powerful run from inside his own half and set up Paul Brooker, who hit his shot straight at Grant.
Derby had to survive four minutes of added time but clung on for a result that keeps their play off hopes alive.