The youth team's unbeaten record came to an end at Glenesk Park on Friday and, in all honesty, Celtic deserved their win.
Whilst there was great debate as to whether the ball had actually crossed the line for Celtic's opener, the truth is that the Tannadice teenagers rarely looked like scoring.
For most of the game United were on the back foot, though it was only late on that Celtic managed to get in behind the back of the United defence, by which time the game was won.
On loan keeper Matthew Curtis from Hibs made his debut and was soon in action as Celtic rained in shots from the outside the box.
Their best first-half effort was a searing strike from striker Cillian Sherian that clipped the outside of the post after 33 minutes.
Indeed, it was United who came closest to scoring three minutes later when a Neil McMechan header from a corner was cleared off the line by Paul Cahillane.
But it was United's turn to make goal-line clearances as Celtic turned up the heat at the start of the second half. Twice Scott Paterson came to the home side's rescue following corners.
It was from another corner on the hour mark that Celtic took the lead when Mark Millar's kick hit the underside of the bar and was adjudged to have crossed the line before it was hacked away.
Ten minutes later the game was put beyond United when Kevin Cawley danced his way to the bye-line to cut the ball back for Sherian to slam in the second from close range.
Team (4-4-2): Curtis, Milligan, McMechan, McGrath, Pope; Paterson (Russell 77), Andreoni, Mathieson (O'Hara 69), Fleming; McCord, eney (Love 77).
Subs not used: Newman, Allan, Gray, McLeod.
A disappointed Stevie Campbell said afterwards, "Perhaps this was a bit of a reality check. The spark that has been the hallmark of the lads play was missing today.
"It has to be said though; this was a very decent Celtic side that played at a very high tempo. For us to have taken anything from the game, would have meant us having to be at our best, which unfortunately, we weren't."