“Today I think was a clear difference in the desire to fight for the targets,” said Mourinho, whose side missed the chance to all but secure second place in the Premier League behind champions Manchester City.

“They clearly showed that, for them, it’s more important for them to stay in the Premier League than for us to finish second. They showed it from the first minute, and we didn’t show that.

“I am disappointed because second is important for me. I’m not sure every one of my players is disappointed.”

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.

With third-bottom Southampton and 17th-placed Swansea to meet on Tuesday, Brighton now can’t now be relegated.

“I felt that we’ve deserved to stay in this league for our season’s work,” said Brighton boss Chris Hughton.

“But if we’d lost today and the next two, it would have been a real feeling of injustice had we gone down. So relief that we’ve done it now, but I’m also really proud of a group of players.”

By contrast, defeat means United must wait to secure second 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.

– ‘I know my players better’ –

“For many months you are always asking me why this player doesn’t play? Why that player doesn’t play? Why this player is on the bench? Why always Lukaku?” added Mourinho.

“I know my players better than you, and probably you don’t know them so well to be always with these questions.”

The visitors did have the ball in the net after just four minutes when Marouane 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 desperate need for the points shone through.

David de Gea was the only United player selected in the PFA’s Premier League team of the year and the Spaniard showed why he has again been his side’s outstanding performer this season with a stunning fingertip save to turn a dipping volley from Glenn Murray behind.

Brighton’s survival party had been put on hold by a run of seven games without a win.

But they got the helping hand they needed from the goal-line technology system to seal another campaign in the Premier League on their return to the top flight after 34 years on 57 minutes.

The dangerous Jose Izquierdo got to the byline 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 Marcos Rojo.

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 and Jesse Lingard fired off target as Brighton held out despite a late United rally.