Man United had scored three goals in the first 31 minutes.
United's Ashley Young had the first two goals.
Substitute Andre Carrillo's crossed for the second goal, which was finished by Abdoulaye Doucoure.
After the half hour there was a third goal when United's Romelu Lukaku picked up Waterford's Christian Kabasele's clearing header.
But it was United's Jesse Lingard that sealed the win for the team.(ANI)