As Barry Robson's side went into game number 29 of 32 in the Under 18 League, another close encounter was expected, each having beaten the other once in Dundee while the third meeting at Cormack Park back in September ended in a highly entertaining draw.
The home side were on the offensive from the off and Duncan's cross just evaded Harvey to deny the Dons a gaol in the opening twenty five seconds.
Another well worked move down the right created an opening for Adam Emslie on nine minutes, but he was unable to make a clean connection and United were able to clear.
A fine ball from Kai Watson was played on by the impressive Finn Yeats to give Emslie a sight of goal, his parting shot going just wide. It had been a bright opening from Aberdeen who were playing a brand of football which was very pleasing to watch.
Tom Ritchie in the home goal was called into action for the first time on 23 minutes, United skipper Moore firing in a fine twenty yard shot as Ritchie made the save look ridiculously easy, a sign of a confident young keeper.
On twenty six minutes the Dons got the breakthrough they richly deserved.
A delightful through ball from Yeats sent Duncan racing clear and he finished clinically, rifling the ball in off the keeper's left hand post. An excellent finish from the big man, but his task made much easier by the quality of the pass from Yeats.
United fought back and Watson did well to block a fierce shot from Rory MacLeod before Duncan's free kick was headed wide by Evan Towler as Aberdeen pushed for a second.
A dangerous cross from United's Thomson found no takers in a tangerine shirt, and within two minutes, Aberdeen had doubled their advantage. A long free kick from Ritchie picked out Duncan perfectly, and when his powerful strike was parried by McCabe, Harvey was in the right place to slam home the rebound, his 13th League goal this season.
A very entertaining first half and the Dons well worthy of their interval lead.
Half time - Aberdeen 2 Dundee United 0
The Dons were at it from the off again following the break, only a flying save from McCabe denying Emslie. And the visitors had their keeper to thank again six minutes later as saved well from Duncan after the big man had been picked out superbly by Dylan Lobban who had another excellent game in the heart of the Dons midfield.
On the hour mark the Dons effectively put the game to bed when tenacious work from Liam Harvey saw the Elgin-born hitman cross for Ryan Duncan to thunder the ball home.
United were refusing to lie down though and Ritchie had to stretch full length to turn away a shot from Moore, but he was left helpless when Donald got a deft touch on a dinked pass from O'Donnell to reduce the deficit.
Understandably the pace of the game dropped towards the end, but Ritchie made a fine save tipping substitute Lovie's swirling cross on to the bar and away to safety before Duncan came within inches of a hat-trick when he met a long clearance of the half volley, the left footed effort so close. It would have been a great goal had it between a foot to the left of where it landed.
Both sides deserve a lot of credit for playing some good football, but Aberdeen were the stronger side and fully merited the win. They now travel to Kilmarnock on Sunday and Celtic on Tuesday to wind up a long campaign which will undoubtedly stand this young group of players in good stead for what everyone at the club hopes will be a bright future.
Full time - Aberdeen 3 Dundee United 1
Barry Robson: "The first 45 minutes, that is as well as we have played. It was pleasing. You could see the style that we were trying to play, the way we pressed the ball, the intensity we played at. I am sure the players enjoyed that first half.
"The game got a bit scrappy in the second half, but a good performance and it could have been more than three.
"Two even teams age wise, so that was pleasing as most of the season we have come up against older sides. It is good to go and play a game when you have two even teams. We have not had Tom, Ryan or Evan for most of the season. It is good to give them some game time before the season ends.
"A good result which was thoroughly deserved."