Nottingham Forest boosted their fight to avoid getting sucked into a relegation battle - and put a dent in Brighton's hopes of escaping the Championship at the right end - as Gary Brazil's side won 3-0 at the City Ground.
Chris Hughton's side had not lost in six games on the banks of the River Trent, but suffered a second consecutive league defeat for the first time since September, as the Reds edged what was often a nervy, scruffy encounter.
Brighton were furious that Forest's first goal was allowed to stand in the 60th minute, with Britt Assombalonga attempting to get the final touch to a goal-bound shot from Zach Clough. The visitors felt Assombalonga had made contact - from a clearly offside position. But the goal was allowed to stand.
Forest made certain of three points as a blunder from David Stockdale handed Ben Osborn a second Forest goal in the 90th minute, before a Clough penalty, six minutes into injury time, added gloss to the scoreline.
The two sides were both desperately in need of points, for very different reasons - and it lead to a cagey, cautious first half, in which neither Forest or Brighton seemed willing to take too many risks.
Jordan Smith had to make a smart save to deny Anthony Knockaert, after he had cut in with purpose from the right side to send a stinging shot across the face of goal, towards the far post.
But it was the home side who were carving out the larger number of opportunities, even if none of them were anything more than half sights of goal from distance.
Jamie Ward had four efforts from the edge of the box on his own, in the form of a free-kick driven straight into the defensive wall, two shots that were deflected wide and another that arrowed high into the stands.
Assombalonga was not too far away with a dipping effort that dropped just wide, but Forest were finding it hard to turn short spells of pressure into clear openings, amid a scrappy, disjointed contest.
A battling determined run from Ward gave him the room to cross from the left early in the second half, but the ball eluded Assombalonga by a matter of inches in the centre.
A Knockaert free-kick was headed back across goal by Lewis Dunk, with Shane Duffy bravely attempting to convert at the far post, only to prod wide and smashing into the frame of goal in the process, as Brighton came close.
But it was Forest who were to take the lead, in slightly controversial fashion. When Matty Cash cut a ball back across the face of the penalty area, substitute Clough's first touch after coming on was a curling shot that was bound for the back of the net. Assombalonga clearly attempted to make a connection to guide it home, but did not appear to touch the ball.
Brighton argued that he had made contact - and that he had done so from a clearly offside position. But the goal was allowed to stand and Forest had a precious lead to hold on to.
Seagulls sub Solly March almost made an immediate impact himself, with a fierce low shot that Smith did brilliantly to push around the post.
While Knockaert might have done better with a late header, after being picked out at the far post by the lively March.
Forest made sure of victory in the 90th minute, albeit with the aid of some serious help from Brighton, who laid a second goal on a plate for their hosts, as keeper Stockdale made a hash of things, as he dealt with a back pass - only succeeding in flicking the ball to Osborn, who slotted into an empty net.
That was not the end of the scoring, as Dunk felled Forest sub Ben Brereton to concede a 96th-minute penalty - which Clough duly converted emphatically.