Albion's dismal record at Roots Hall continued with a disappointing 2-0 opening day defeat.
Goals at the start and finish by Martin Carruthers and David Lee settled a competitive seaside showdown.
A bumper crowd of 7,492, basking in sweltering conditions, saw Carruthers deliver a damaging blow in the fifth minute.
His downward header from Damon Searle's cross following a short corner routine left the Seagulls on course for their eighth successive defeat in visits to the Essex club.
Former loan capture Bobby Zamora, re-signed from Bristol Rovers for £100,000, had Albion's best effort of the first half, his shot forcing Andy Woodman into a good save.
Manager Micky Adams decided to make changes at the break, bringing on Darren Freeman for captain Paul Rogers and Mark Cartwright in goal for Michel Kuipers.
The Seagulls started the second half more purposefully, Hart also having a shot saved by the on-loan Woodman.
Albion's loan keeper Cartwright then kept them in the match, the Wrexham man foiling Neil Tolson and Martyn Booty in impressive fashion.
Cartwright could do nothing though about David Lee's 83rd minute clincher.
The 20-year-old midfielder, making his League debut after a summer move from Spurs, beat him with a curving effort from 25 yards after Richard Carpenter gave the ball away.
Lee Steele, another of Albion's new boys, replaced Hart midway through the second half, but Lee's strike destroyed any hopes of a comeback.
The 3,500 Albion fans filtered sombrely out of the ground at the finish, in stark contrast to their celebratory mood prior to kick-off.
See Monday's Argus for verdict, reactions, pictures and match facts from Roots Hall.
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