Brighton secured their place in the Premier League next season as Pascal Gross's solitary goal inflicted a 1-0 defeat on Manchester United on Friday.
Just over two weeks ahead of the FA Cup final against his old club Chelsea, United manager Jose Mourinho made six changes and was punished as Brighton recorded their first win over the Red Devils since 1982.
Chants of "we are staying up" rang around a packed house at the Amex Stadium at full-time as victory moved Brighton up to 11th and more importantly eight points clear of the bottom three.
The theme tune to the World War II movie 'The Great Escape' also rang around the stadium as the players celebrated after an epic effort.
With third bottom Southampton and 17th-placed Swansea to meet on Tuesday, Brighton now can't now be relegated.
By contrast, defeat means United must wait to secure second place as they remain five points clear of Liverpool with Tottenham a point further adrift.
United were without either of the injured Romelu Lukaku or Alexis Sanchez, and their firepower was missed as Anthony Martial and Marcus Rashford failed to make the most of rare chances to start up front.
The visitors did have the ball in the net after just four minutes when Marouanne Fellaini turned Rashford's free-kick in from close range, but the Belgian was rightly flagged for offside.
United secured a top-four finish by beating Arsenal 2-1 last weekend, and Brighton's more desparate need for the points shone through.
David de Gea was the only United player selected in the PFA's Premier League's team of the year and the Spaniard showed why he has again been his side's outstanding performer this season with a stunning finger tip save to turn a dipping volley from Glenn Murray behind.
At the other end Lewis Dunk bravely put his head in the way of a powerfully struck effort from Rashford, but then presented possession to the English international on the edge of his own box moments later.
Rashford's indecision in failing to pick out Martial or go for goal himself, though, summed up a frustrating night for United with Mourinho quick to show his discontent on the sidelines.
Brighton's survival party had been put on hold by a run of seven games without a win.
Goals have been hard to come by for Chris Hughton's men in their first season back in the top flight for 34 years.
But they got the helping hand they needed from the goal line technology system to seal another campaign in the Premier League on 57 minutes.
The dangerous Jose Izquierdo got to the by-line and when his cross was parried by De Gea, the ball crossed the line from Gross's header by the finest of margins before being hooked clear by Marcus Rojo.
Brighton's tails were up and they could even have added to their lead when Izquierdo fired inches wide moments later.
Victory would have virtually guaranteed United second place behind champions Manchester City.
Instead, City can now break United's record winning margin of 18 points from the 1999/2000 season should they win their remaining three games.
Matt Ryan saved well from Rashford before Martial fizzed a shot inches over as Brighton held out despite a late United rally.
Rashford teed up substitute Jesse Lingard for one final chance to spoil Brighton's party six minutes from time.
But against his former club, Lingard fired wide to condemn United to a seventh Premier League defeat of the season.