He said: "This is a group of players with great belief and discipline".
The team from the south coast are eight points clear of 18-place Southampton and 17-place Swansea.
"We learned after the first few games that the performances were good enough and we weren't always going to get beat, and that gave us confidence".
Martial and Rashford replaced Lukaku and Alexis Sanchez in United's line-up against Brighton but failed to impress as they lost 1-0.
Mourinho comments after the match about Manchester United performance only reinforced Neville's comment that he lost faith in some of his team players. "But now we need four points and we must try to get them".
But they were only able to create one chance in the entire first half, while their first shot on target came through Paul Pogba in the 49th minute.
"I am disappointed because second is important for me".
"I am not sure what was wrong".
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The duo exchanged one of the best post-game-winner high-five and finger-pointing sequences you will ever see. "Tie game. Casey said his team played with "our trousers on fire defensively", but struggled to take care of the ball on offence.
The Belgian, whose future remains uncertain with his contract nearly up, had the ball in the net after only three minutes but he was offside when he turned home Rashford's free kick.
Lukaku picked up an ankle injury during Manchester United's 2-1 win over Arsenal last week and has travelled to Belgium for treatment.
"It's a relief because even going into the game I felt, for our season's work so far, that we deserved to stay in this league".
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 worldwide on the edge of his own box moments later. Maybe now you will not ask me why A, B and C do not play so much. Why this player is on the bench?
"People always ask 'Why always Lukaku?" Why always this? You have the answer why always this!
Brighton's survival party had been put on hold by a run of seven games without a win.
Chris Hughton's side can now look forward to another season in the top flight having assured they are mathematically safe ahead of trips to Manchester City and Liverpool.
Izquierdo's cross found Gross six yards out from goal and the playmaker's header went just over the goal-line, despite Marcos Rojo's despairing efforts to keep it out.