In the 38th minute of a turgid SPL encounter, Dennis Wyness opened up the Ayrshire defence with a clever pass giving Dorman the chance to drive low past Killie keeper Alan Combe.
The home side huffed and puffed in an equally poor second half but the Paisley side held on to record their third SPL win in a row for the first time.
St Mirren manager Gus MacPherson, who celebrated five years in permanent charge of the Buddies this week, will not care, but it must have been a long time since any of the 5183 crowd had witnessed such a poor game.
The first half, in particular, was best forgotten, Saints' goal aside.
It was Wyness who registered the first effort on goal of the afternoon after three minutes when he curled a shot from 20 yards in to the arms of Combe.
But the home side responded positively and amid a brief but intense spell of pressure, only a block from St Mirren defender Jack Ross prevented Allan Russell's drive from 12 yards finding the net.
The game developed in to a dour struggle, niggling fouls interrupting any possible flow with too little football being played in between.
In the 26th minute, Killie wide-man Garry Hay chipped the ball in to the box where Allan Russell knocked it down to strike-partner Donovan Simmonds.
In one move, the big striker, on loan from Coventry, turned and sent a volley from 14 yards dipping just over the bar.
But Killie could not build on that isolated moment of skill, failing to make another impression until 10 minutes before the break when Russell had his angled shot from 18 yards easily saved by Mark Howard.
And in the 38th minute, with the first half seemingly destined to be goalless, the visitors took the lead with a well-worked goal.
Wyness took a Franco Miranda pass at the edge of the Killie box and played a clever pass in to the path of Dorman who drilled his shot from 14 yards under Combe and in to the corner of the net.
The move and the finish shone like a beacon amid the enveloping Rugby Park dullness.
To compound the blow, Killie defender Frazer Wright came off immediately after with an injury to be replaced by Craig Bryson and another reshuffle ensued.
Killie could have felt aggrieved at being down at the interval.
Certainly, midfielder Gavin Skelton's wild, speculative shot 20 seconds after the restart which went well wide of the target indicated their determination to get back level as soon as possible.
But the turgid football that characterised the first half quickly returned, with both teams culpable.
The Killie supporters became frustrated, taking their wrath out on referee Steven O'Reilly for any perceived mistake by the official.
In the 57th minute Dorman had another effort after Hamilton knocked the ball down to him inside the Killie penalty area but this time his left-footed shot was easily gathered by Combe.
Moments later, the Rugby Park keeper had more to worry about when Ross's drive from 30 yards skimmed his right-hand post.
In the Jefferies brought on Iain Flannigan for Jamie Hamill while MacPherson replaced Jim Hamilton with Billy Mehmet.
Killie swarmed around the edge of the St Mirren box without making Howard work and with that in mind, Jefferies then brought on Conor Sammon for Russell with 10 minutes remaining.
The dying stages witnessed an increase in desperation from the home side but it was St Mirren who almost doubled their lead with three minutes remaining, Garry Brady's curling shot crashing off the post before Combe blocked Mehmet's shot from the rebound with his legs.
A last-minute tackle by St Mirren defender Scott Cuthbert stopped Sammon going through on goal and with that, Killie's last real chance was gone.