Ryan Dow capitalised on a dreadful pass back by Ash Taylor to open the scoring before Gary Mackay-Steven doubled the lead just before the break.
The Dons toiled in the final third though Niall McGinn hit a post in their most clear-cut opportunity.
Chris Erskine completed the hammering with a calm finish at the death.
But for a 5-2 reverse at Celtic Park last season, this was the heaviest defeat of Derek McInnes's Pittodrie tenure.
His team has again been tipped to finish second this season, but the profligate issues of last campaign continue to cause him a headache.
The Dons had benefitted from playing competitively for the last month thanks to their European campaign.
But that was cancelled out by what was an energy-sapping defeat to Real Sociedad on Thursday.
Skipper Russell Anderson and winger Jonny Hayes missed out through suspension and former United striker David Goodwillie was again preferred to Adam Rooney up front.
United were shorn of two of last season's stars Ryan Gauld and Andrew Robertson, who made big money summer moves to Sporting Lisbon and Hull City respectively, as well as defender Gavin Gunning.
Captain Sean Dillon will be missing for six weeks due to a broken cheekbone sustained in pre-season.
Jackie McNamara handed competitive debuts to Jaroslaw Fojut, Callum Morris and Conor Townsend as he patched up his defence.
And it was the Tangerines who began the brighter of the two with the movement of Nadir Cifci, Mackay-Steven, Dow and Stuart Armstrong causing problems.
The Dons had the first good chance as Taylor flicked the ball towards Andrew Considine, who volleyed over.
United took the lead just before the half-hour mark and it owed much to the generosity of Taylor.
The new Dons defender gift wrapped it for Dow with a slack pass into his own box and the latter nipped onto it before firing home to the delight of a boisterous away end.
The goal appeared to wake Aberdeen up and McGinn saw a volley hit the post after Radoslaw Cierzniak came and missed a Barry Robson cross.
Just as the Dons began to dominate, United doubled their lead and it was a wonderful counter-attacking move that provided it.
Erskine slots by Jamie Langfield to seal United's victory
Ciftci sprayed a superb pass with the outside of his boot through to Mackay-Steven and the former Liverpool trainee capitalised on a static home defence to slide it under Jamie Langfield on the stroke of half-time.
Aberdeen were one of the teams a free-flowing United struggled against last season but McNamara's tactics suggested he had learned from those games.
Ciftci and Dow both had other counter-attacking chances in the second period as they continued to open up the Dons defence.
Aberdeen dominated possession but their cutting edge was lacking, and but for two penalty shouts and a block on the line by Morris, they failed to unduly threaten Ciezniak.
The first was a challenge by the Polish keeper on substitute Rooney, the second a handball by Morris which Willie Collum turned a blind eye to.
United continued to soak up the limited pressure and completed the scoring after a brilliant run from another debutant.
Substitute Mario Bilate drew the Dons defence out and put in on a plate for Erskine, who calmly finished from around the penalty spot.
United were impressive going forward, but a first clean sheet since December will equally please McNamara, particularly so given 75% of his defence was untested competitively.
The result and performance has brought the Dons back down to earth after a promising European adventure.