After a lively start by both sides, Fernandes gave the Reds a deserved first-half lead on 27 minutes - netting his 20th goal of the season - when he pounced on a collision in the Real Sociedad backline between two defenders and their goalkeeper.
Fernandes doubled our advantage just before the hour-mark, following a fine move involving Rashford and James, before Rashford added the third soon after, latching on to a lovely pass from Fred to finish with aplomb.
After Amad came on for his United debut, James rounded things off in excellent fashion when he drove into the box from the right wing before squeezing his shot in from a tight angle.