Marcus Rashford, Juan Mata and Luke Shaw came onto the field during the second half of the game and all three had a huge impact as United came 2-0 down to win 3-2 in injury time.
Mourinho feels all three substitutes had a huge impact on his team coming back to win against Palace
The win keeps United in second place ahead of their showdown with Liverpool to come on Saturday and Mourinho feels the win wouldn't have been possible without the tactical moves that the substitutes had on the team.
Mourinho started by saying that "Marcus was good" when he came on for Scott McTominay at half-time as he "immediately created dangerous situations and opened more spaces" for other players to get into and that caused chaos for the Palace defenders.
The United boss continued to say that to win the game "we had to take risks" like moving Jesse Lingard to right-back to be "an extra man attacking other areas" which caused a different type of problem for the Palace players.
The importance of the win was key in the battle for second in the Premier League
Mourinho added that all these changes made it "difficult" for Palace to cope and that made Roy Hodgson change things around by bringing on "Riedewald to play wide and cover" Lingard but with "Mata coming to the inside" it meant that we could "create a lot of problems in the second half" which helped the team get a vital victory.
The comeback win against Palace marked the second successive win for United after being in a losing position which is important given how close the fight to finish second in the Premier League is currently with nine games to go.