Tomer Hemed scored his second goal of the season to bring Newcastle's run of three consecutive Premier League wins to a shuddering halt.
The Brighton forward netted after 51 minutes after Dale Stephens knocked down Pascal Gross' free kick.Rafa Benitez threw on Jonjo Shelvey and Dwight Gayle for the closing stages but his disappointing team were unable to force the equaliser.
The former Liverpool midfielder hit the post directly from a corner after 73 minutes.
It was sweet revenge for manager Chris Hughton who was ruthlessly sacked by Newcastle after three years – and had not beaten his former club since.
The defeat sees Newcastle, who started the weekend in fourth place, slide to ninth while Brighton are up to 13th after a second home win of the season.
The visitors, who did the double over Brighton last season, started brightly and Matt Ryan save from Mikel Merino in the second minute.
Joselu spurned Newcastle's best chance of the opening period while at the other end, Pascal Gross' goal-bound shot hit Anthony Knockaert. The crowd of 30,486 was a new record for the Amex Stadium.
Here is how all the action unfolded....
Early team news
Bruno, Glenn Murray, Izzy Brown and Gaetan Bong will all be available for Brighton when they host Newcastle on Sunday.
Bruno was absent for last Friday’s defeat at Bournemouth, owing to a back injury, while Murray missed out on Tuesday’s loss to the same team because of an injured ankle.
A back injury means Steve Sidwell remains unavailable, while Beram Kayal is a long-term absentee having broken his leg.
Newcastle boss Rafael Benitez has no fresh injury concerns as he goes in search of a fourth successive Premier League win.
Florian Lejeune is yet to fully recover from the ankle injury he suffered against Tottenham during the opening weekend of the campaign, while fellow defenders Paul Dummett (hamstring) and Massadio Haidara (knee) continue to work their way back to fitness.
Striker Aleksandar Mitrovic completes his three-match man, while midfielder Jonjo Shelvey looks for his first start since returning from his own suspension.