After an opening eight minutes of scrappy play, Noel Hunt celebrated his call-up into the Republic of Ireland B squad with a simple goal.
A long Garry Kenneth throw was nodded into the path of the striker who turned and smacked a low eight-yard drive under the body of Alan Combe.
It should have been 2-0 four minutes later when Jordan Robertson scooped the ball over from only two yards after Combe had superbly clawed Prince Bauben's shot away.
United continued to dominate in a completely one-sided half, creating a number of chances most notably Darren Dods' astonishing miss in the 36th minute.
Sean Dillon's corner was remarkably headed wide by the captain when, from two yards out it seemed a certain goal.
After Hunt had opened the second period with a thunderous 25-yard free-kick, Killie manager Jim Jefferies brought on his three substitutes but they did little to change the shape of the game.
The only saving grace for the Ayrshire men was the lethargy of United in the second period. After embarrassingly out-playing their opponents in the first half, the Tangerines were going through the motions in the second.
With their slackness, the hosts were fortunate not to be pegged back when a superb volley from Gary Wales was parried away by the keeper.
United had the chance to make the game safe in the 85th minute when Ryan O'Leary brought down Bauben for a penalty only for Hunt's strike to be well-saved by Combe.
In frustration young Jordan Robertson was red-carded for a push on the keeper. However, it was game over in the 90th minute when Hunt was given acres of space to slide the ball in for a simple Bauben tap-in.