Brighton could have moved eight points clear of Cardiff, which occupies the final relegation spot in the table, with a win on Wednesday (NZST), yet it was the Bluebirds who triumphed thanks to goals from Nathaniel Mendez-Laing and Sean Morrison.
The Seagulls may well point to what appeared to be a clear penalty not given their way, but Chris Hughton's side were punished for missing a glut of early chances when Mendez-Laing struck midway through the first half.
And its hopes of a comeback were dashed five minutes after the restart, visiting captain Morrison heading home to move Cardiff to within two points of its rival, albeit Brighton does have a game in hand.
Attacking intent was in no short supply from the off - Solly March twice drilling wide either side of a wayward Glenn Murray effort, while Joe Bennett went close with a looping cross-shot at the other end.
Brighton had a strong claim for a spot-kick when Lewis Dunk was hauled down by Bruno Ecuele Manga, but the hosts' appeals were ignored by referee Andre Marriner.
Cardiff made their good fortune count in the 22nd minute, Mendez-Laing charging forward from deep before curling an exquisite finish beyond Mat Ryan.
Their lead was doubled early in the second half, Morrison taking advantage of dreadful marking to head in Victor Camarasa's free-kick unchallenged.
Murray lifted a difficult chance just over as Brighton pressed to get back into the contest, but it was not until the 93rd minute that the striker would get another opening, heading against the woodwork, as Cardiff held firm to claim what could prove to be three vital points.