Following successive U18 Premier League South victories over Arsenal and Swansea City, the young Foxes are currently enjoying a brilliant patch of form on two fronts.
However, at half-time in Manchester, their chances of commencing their Group F campaign with a positive result seemed remote after United had opened up a 3-0 lead at Aon Training Complex.
Mark Helm, Ben Hockenhull and Dillon Hoogewerf struck for Man Utd's youngsters and, while Tom Sams momentarily narrowed the deficit after the break, Shola Shoretire made it 4-1 on 50 minutes.
With it all to do in just 15 minutes, the comeback began with Ethan Fitzhugh before Will Russ and then Shane Flynn, from the penalty spot with four minutes remaining, stunned United and sealed a point.
"Everybody is beating everybody at Under-18s level this season, which has been reflected in our results so far this season," said Lead Professional Development Phase Coach, Trevor Peake.
"We're quite strong in the midfield area and we've seen that come to fruition throughout the season so far and it's been great to see us score so many goals over recent weeks."
City and United share the top two positions in Group F, with Brighton & Hove Albion and West Bromwich Albion yet to play, with a point apiece before the U18 Premier League resumes next weekend.
The young Foxes welcome third-place Chelsea to Belvoir Drive next Saturday (12pm BST kick-off) before heading to Southampton seven days later (12:30pm BST kick-off).