Victory lifted John Robertson’s side above Falkirk on goal difference and cut the gap on the Tangerines to 11 points with a game in hand.
More significantly, it sliced the gap on play-off contenders Morton to 12 points, with three games in hand for the Highlanders offering a route back into the hunt.
United, with just one win in the last eight outings, sank deeper into damaging form.
With all the crisis talk surrounding Csaba Laszlo’s United, it was easy to forget at the outset they were the team embedded in the Premiership play-off zone and Caley Thistle, at kick-off, stood a full 14 points behind them.
Robertson’s side, jubilant after Irn-Bru Cup final success, were just four points above second bottom Dumbarton as play began and as much looking to ease relegation fears as relaunch the promotion dream.
Chances were sparse and creativity thin on the ground, but a Coll Donaldson free-kick from deep created a home opportunity after 17 minutes. Nathan Austin’s pace took him away from the United defence but the connection on his header was weak and easily gathered by Harry Lewis.
An incredible Caley Thistle miss followed after 22 minutes. Another terrific turn of pace from Austin set him free to the right of the United box and his chipped attempt beat Lewis and may have been going in. Striker George Oakley met it with his head two yards out and somehow skied the finish over the bar.
Just as the first half seemed to be petering out, the hosts found the breakthrough a minute before the break.
Oakley peeled free of his marker to the right and slipped a clever disguised pass into the path of Doran to fire in low off the keeper’s body.
Sixteen-year-old Daniel MacKay, fresh from a goal in Scotland’s victory against England schoolboys and a cup final assist, entered the fray after the hour – and almost scored two minutes later. Twisting onto his right foot on the left side of the box, MacKay’s fierce, angled strike drew a fine parry for a corner from Lewis. Doran’s corner dipped dangerously across the six-yard box without takers.
Moments later, MacKay clattered heftily through United’s Jamie Robson and was booked.
The hosts might have doubled their lead 11 minutes from time as they went through three-on-two on United but, when Oakley threaded a short pass wide for MacKay, his strike was shut down superbly by the diving Lewis.