Richard Brittain fired the visitors ahead with an excellent 25-yard free-kick and the Highland side passed up numerous opportunities to extend their advantage during the first half.
St Mirren were rewarded for a bright start to the second half when Steven Thompson rocketed a shot past Mark Brown from just inside the area, but it was to be the highlight of the afternoon for Danny Lennon's side.
Sam Morrow took advantage on a horrific defensive error by David Barron to restore County's lead and Ivan Sproule marked his debut with a goal four minutes later.
Sproule capped off an excellent display when he tapped home a fourth and a miserable day for St Mirren was completed when Lewis Guy's penalty was saved by Brown in injury time.
Craig Samson comfortably gathered Grant Munro's header in the opening minute as the visitors demonstrated an early attacking intent.
St Mirren responded positively and debutant Conor Newton laid on Thompson, who saw his effort kept out by the feet of Brown.
Sproule was released by Brittain after Newton clumsily conceded possession, however the County debutant opted to shoot when Rocco Quinn was well placed inside the area.
Sproule was enjoying a lively start to his debut and Graham Carey was forced to bring down the former Hibernian midfielder on the edge of the box in order to prevent him continuing his charge towards goal.
Carey received a booking for his careless challenge and the hosts had Samson to thank for not being punished further - the keeper diving full stretch to keep out Iain Vigurs' free-kick.
Barron fired just wide of the target before Sam Parkin passed up a glorious opportunity when he headed directly at Brown from close range.
St Mirren conceded another dangerous free-kick after 24 minutes when Marc McAusland was adjudged to have handled Quinn's shot and this time the home team were punished as Brittain curled an excellent right-footed strike beyond the helpless Samson.
Derek Adams' side were playing with a great deal of confidence and Sproule came close to doubling their lead with a shot that sailed just past the left hand post.
Jim Goodwin was fortunate to escape a yellow card just before half-time when he carelessly lunged at Sproule, but it was the home fans who reacted angrily, claiming the winger had taken a dive.
Danny Lennon replaced Newton with Dougie Imrie during the break and the change in attacking personnel paid off quickly as Saints drew level within five minutes of the restart.
A patient period of possession was completed in style as Barron picked out Thompson who lashed the ball home from just inside the box.
Guy was introduced in place of Parkin and after spending much of the game on the back foot, it was suddenly the hosts who looked the more likely to add to the scoring.
Referee Euan Norris brandished his second yellow card of the match after Vigurs' poorly-timed tackle on Barron.
Adams made a change of his own just after the hour as Gary Glen made way for Morrow.
Sproule dragged a shot just wide of the target before Morrow made an immediate impact - taking advantage of Barron's poor headed back pass and slipping the ball past the onrushing Samson.
Things got even worse for Saints four minutes later when Vigurs stole the ball from Robertson and when he found Sproule the Northern Ireland international fizzed the ball into the bottom left hand corner of the net.
St Mirren had been controlling proceedings before falling behind for the second time in the match, but seemed to have lost all composure after conceding twice in four minutes and they conceded another goal with 16 minutes to go.
Brittain's corner broke to Quinn who unleashed a powerful shot that Samson could only parry and Sproule was on hand to coolly finish.
Both sides made changes as Paul McGowan was withdrawn and John McGinn introduced, while Sproule walked off to a great ovation from the small band of travelling supporters with Steven Ross coming on.
Gary Teale forced Brown into a good stop as St Mirren looked for a consolation and they were presented with the perfect opportunity when they were awarded a penalty in injury time.
Lewis Guy stepped up but was denied by an excellent save from Brown.
- Sports & Recreation