Marcos Alonso scored the only goal of the game as Albion were squeezed out at Bolton Wanderers.
The result means the Seagulls slip out of the play-off positions and to add to the disappointment, Ashley Barnes was shown a late red card by referee Nigel Miller.
Barnes was one of five changes to the side that drew a blank with Bristol City on Tuesday night, with Andrew Crofts – making his first start since December – Vicente, Wayne Bridge and Leonardo Ulloa returning to the starting line-up.
Although the Seagulls were the visitors at the Reebok Stadium, the roles seemed reversed as Gus Poyet’s men made all the running while Bolton seemed content to sit back and rely on counter-attacking football.
Liam Bridcutt – skippering the side just days after his first Scotland call-up – looked to have unlocked the Bolton defence when his chipped ball landed at the feet of Barnes, but as the Albion striker pulled the trigger Zat Knight slid in with a well-timed challenge to defuse the effort.
But moments late the home side showed their attacking threat when former Liverpool striker David Ngog skipped past Bridcutt before turning inside Matthew Upson, but his weak effort was stopped with ease by Tomasz Kuszczak.
The game was of contrasting styles with the slick Albion competing against a powerful and towering Bolton side, but it was Barnes who got the run on Knight inside ten minutes to meet Bruno’s cross - his glancing header though went narrowly over.
Albion asked questions of the home defence in set-piece situations; first it took a smart save by Andrew Lonergan to deny Crofts’ well-struck volley then David Lopez picked out Ulloa whose header had the Bolton defence scrambling.
The ball was only cleared as far as Bruno who cut the ball back to Crofts from the by-line but his 12-yard effort bounced back off the post before being cleared.
On 20 minutes came the opener through left-back Alonso. He cut in from the left and his shot from the edge of the box skimmed past a bunch of players before nestling in the bottom right corner.
Bolton – chasing the Seagulls for sixth spot – could have doubled their lead on the brink of half-time when the impressive Alonso picked out Ngog with a near-post cross which was stabbed over from close range.
Within Nottingham Forest beating Wolves, the Seagulls came out for the second half knowing that they needed points from the game to keep their place in the play-offs. David almost levelled in spectacular fashion when his well-timed volley shaved the Bolton crossbar with Lonergan rooted, while moments later Ulloa’s back-post cross was ballooned over by Barnes on the volley.
Bolton still showed potent signs in the Albion box and it took committed defending by Adam El-Abd
and Bridcutt to block the efforts of Chung-Yong Lee and Jay Spearing respectively.
Poyet said that he would take risks if required and he showed that when he introduced wingers Will Buckley and Andrea Orlandi at the expense of Bridge and Crofts and it took little time for Buckley to start causing the home side problems down the right with some teasing runs.
Indeed, he was brought down wide on the right which set up another free-kick; David provided the inviting delivery but Ulloa’s header evaded the Bolton goal.
Buckley again sparked an attack with five minutes remaining, linking up with Vicente, who picked out Orlandi at the back post. The former Swansea man cut inside onto his right foot but his curling effort – anticipated for the top right corner – went narrowly wide.
Albion pushed hard in search of the equaliser but time ran out, although hearts were in mouths among the home fans when Bridcutt’s late effort was initially fumbled by Lonergan and Buckley’s left-footed volley went narrowly wide.
To rub salt into the wound Barnes was shown a straight red card in the dying seconds, which leaves Poyet with just one available striker. Albion can reclaim sixth spot with a win at Barnsley on Tuesday night.