Fit-again Jon Daly came off the bench to score with his first touch of the ball to secure a hard-fought win over Inverness Caledonian Thistle.
United goalkeeper Dusan Pernis denied Gregory Tade before on-loan Fulham forward Lauri Dalla Valle fired the hosts ahead after 13 minutes.
Nick Ross forced in an equaliser from Tade's cross three minutes later.
But Danny Swanson's lofted finish two minutes from the break and Daly's 71st-minute header won it for United.
United manager Peter Houston had resisted the temptation to start Daly following the striker's quicker than expected return from knee ligament damage and Ryan Dow was given the job of replacing the suspended Johnny Russell.
And the young forward threatened within a minute only for his shot to be blocked by Roman Golobart.
But Inverness, with Greg Tansey preferred to Gavin Morrison in midfield, were the more threatening side early on and Pernis turned wide a Tade drive.
From the corner, Andrew Shinnie flashed a header wide.
United went in front when Dalla Valle made room for himself before firing low and hard across goalkeeper Ryan Esson for the Finnish striker's first goal since arriving on loan from Fulham.
Inverness composed themselves and were level within three minutes when Tade's cross following some poor United defending was forced over the line by a combination of Ross and United's Paul Dixon.
Dalla Valle was denied a carbon copy of his opening goal as Esson superbly turned the striker's shot wide.
Swanson squandered a chance when he fired across the face of goal with Caley Thistle claiming a hand ball against Willo Flood.
However, the United winger made no mistake as half-time approached when Tade lost possession inside his own half and, when defender Golobart hesitated, Swanson gathered the ball and lifted it over Esson.
The former Berwick Rangers man was the first to threaten after the break with a drive from the edge of the penalty box that stung the hands of Esson.
Caley Thistle's goalkeeper was forced to concede a corner when United defender Gavin Gunning tried an audacious 40-yard drive that was touched wide by Esson.
Tade should have done better at the other end when the striker's pace took him clear of the United defence, but his effort was blocked by the feet of Pernis.
Daly was introduced to the action in place of Dow after 68 minutes and, with his first touch of the ball, the striker headed United further ahead from a Dixon cross.
Graeme Shinnie fired over from close range for Inverness in the closing minutes, but United were already home and dry.