The Under-18s secured progression to this stage with victories at home to Scunthorpe United in December and away to Reading in January.
Managed by lead coach Travis Binnion, United showed a ruthless steak in the fourth round in Berkshire as Kobbie Mainoo, Sam Mather and Charlie McNeill scored to earn a three-goal first-half lead. Reading got a deserved consolation late on but it was a comfortable victory for the Reds.
In the third round, Alejandro Garnacho lit up Old Trafford with an acrobatic finish in front of the Stretford End. Further goals came from Mather, Maximillian Oyedele and McNeill in a 4-2 win against Scunthorpe.