Goals from Guy Butters and new boy Chris Iwelumo sent Chesterfield crashing to their first defeat at Saltergate since October, on a night when a swirling wind and a controversial display from referee Martin Atkinson dominated.
The Leeds official let a blatant handball from visiting keeper Ben Roberts well outside his area go unpunished in the 31st minute and that was the only real talking point of a desperately poor first half. Brighton, with skipper Danny Cullip outstanding, defended well and limited the Spireites to few chances although the visitors also failed to threaten going forward.
It was different after the break, when Butters scored for the first time since September to put the Seagulls on their way to a rare away win. The centre-half met a corner from Nathan Jones with a header at the back post from inside the six-yard box and from then on, Brighton always looked comfortable.
Butters headed another corner, this time from Richard Carpenter, against the crossbar in the 75th minute and although Chesterfield kept going, the visitors defended strongly.
The goal that settled the game was the highlight of the night with Iwelumo celebrating his move from Stoke with an outstanding strike. The big centre-forward cut in from the Chesterfield right and went past two players before unleashing a right-foot shot from 25 yards that flew into the top left hand corner.
That sealed Brighton's first away win since November although Chesterfield might have pulled a goal back in the final minute.
Glynn Hurst muscled his way through on the right but Roberts was quickly off his line to block the striker's shot, although Chesterfield will argue he should not have been on the field.