Desperate to improve upon their poor home record of only one win in eight SPL outings in the Highland Capital, Inverness were forced to survive a few scares before eventually imposing themselves on proceedings.
Headers by Jon Daly and Garry Kenneth, both from Danny Swanson corners, gave the visitors the impetus early on, but Caley Thistle battled back and had two chances in the space of as many minutes to open the scoring.
Richard Hastings' 13th minute cross was not cleared by the United defence and that allowed Andrew Barrowman to steal in and unleash a smart first-time effort that only just bent narrowly wide of the post.
Inverness continued to press and in the 15th minute Don Cowie found himself in on goal from Dougie Imrie's lofted ball over the top, but the ball would just not sit down for the midfielder and his attempted lob dropped harmlessly over the crossbar.
The best chance of half fell to United, however, just past the midway point. Kenneth's ball for Daly looked hopeful yet he took advantage of a slight slip by Proctor to control the pass only with his next touch to balloon his shot high into the stand from just inside the 18-yard box.
But Daly made amends six minutes into the second half, powering home a fine header from eight yards after he had stolen a march on the rest of the Caley Thistle defence to get on the end of Swanson's free-kick.
United were now on the ascendancy and looked to have put the game beyond Inverness with a second goal on 64 minutes.
This time Daly turned provider, setting up Craig Conway, who turned his marker superbly before smashing the ball into the bottom corner past a despairing Ryan Esson.
After Conway had been denied by Esson when clean through, his resultant corner produced a third goal on 71 minutes, David Robertson heading home to put United well in control.
Two minutes later, however, Caley Thistle gave themselves a lifeline, Adam Rooney superbly volleying home Cowie's cross to give the home side a glimmer of hope.
But it was all to no avail, as United comfortably held out to make it six games unbeaten against an Inverness side frantically struggling to find some form on their own pitch.