The win was spearheaded by skipper Bruno Fernandes, on the night he made his 250th appearance for the Red Devils, as the Portuguese scored the first and assisted Alejandro Garnacho's goal.
United's first goal in the game came at the 17th minute mark when Fernandes exchanged a quick one-two with Amad before the captain wrapped the ball perfectly around Hermansen's reach from the edge of the box.
United capped a strong half with a second with just over five minutes left before the interval. Noussair Mazraoui picked up the ball on the left flank and whipped in ball to the centre of the six-yard box that the Foxes struggled to deal with.
Fernandes got a touch to it but the decisive flick was off Kristiansen's thigh that diverted it on target, and hence meaning own goal by the defender and a two goal lead for the hosts at half-time.
The second 45 minutes were seemingly lacklustre compared to the first half with both sides struggling to create anything in the final third and the scoreline did not change until the 82nd minute.
Alejandro Garnacho received the ball just outside the penalty area on the end of a driving midfield run from Fernandes. He got the ball out of his feet and curled it faultlessly into the top right corner, leaving a diving Hermansen hopeless and sealing the win for the Red Devils.
Manchester United remain in the 13th spot in the Premier League table but have showed plenty of potential to new incoming head coach Amorim. The Portuguese will be taking charge of his first game as the man at the helm after the international break against Ipswich Town.