Hamilton midfielder James McCarthy crashed a shot off the post two minutes before the break after Kenny Deuchar had fired over the crossbar from close range.
There was little improvement after the break although Garry Brady wasted a decent chance to grab the breakthrough for the lacklustre visitors when he blazed over from 12 yards.
Eight minutes from time, as Dargo raced through on goal, Cerny brought the former Killie player crashing to the ground outside the box, leaving referee Stephen Finnie little option but to show him the red card.
St Mirren might have been expected to be buoyed by confidence after their Homecoming Scottish Cup win over Celtic in their last outing a fortnight ago but they were slow out of the traps.
In the fifth minute, after McCarthy had helped the ball forward, St Mirren left-back Mo Camara almost allowed Joel Thomas in when he failed to put enough on his headed pass-back but Mark Howard came quickly out to smother.
The Paisley side stepped up their work rate and five minutes later right-back Jack Ross stormed forward to send his low drive from 25 yards wide, moments before midfielder Steven Thomson ended a spell of pressure on the home side's goal when his attempt from the edge of the box was saved by Cerny.
The Lanarkshire side should have taken the lead in the 26th minute, however, after Thomas' industry led to the ball dropping at Deuchar's feet eight yards out.
But the former Gretna striker slashed wildly over the crossbar to the groans of the home fans.
Ross had another go from the same distance after Brady's pass had travelled across the Accies box unhindered but he blazed over the top.
Two minutes from the interval McCarthy found a yard of space inside the St Mirren box after slipping past Scott Cuthbert but although his left-footed shot beat Howard, the ball crashed back off the post and Cuthbert recovered to clear.
Five minutes after the break it was McCarthy again causing problems when he reached the byline and stood the ball up at back post leaving Ross to desperately head clear under the crossbar with Deuchar lurking.
Paul McGowan came on for Deuchar in the 54th minute but seconds later St Mirren striker Billy Mehmet made his first significant contribution when he was first to Camara's whipped-in free-kick, but Howard was untroubled with the header.
Minutes later Mark McLaughlin was booked by Finnie for complaining too long and loud when the referee had turned down a penalty claim after Mehmet clashed with Chris Swailes inside the six-yard box, following a McGowan corner.
Seconds later, Thomas' toe-poke from six yards hit the side-netting, after he had been set up by James McArthur.
The Paisley side remained subdued but in the 63rd minute Brady blasted over the bar from 12 yards, wasting their best chance of the second half.
Stephen McGinn replaced Gary Mason with around 20 minutes remaining as Buddies' boss Gus MacPherson tried to shake his side up and the midfielder had two shots from close range in quick succession, his first blocked by sheer numbers inside the Accies box with his second drilled wide.
Hamilton responded by throwing on Jordan McMillan for Grant Evans but it was Saints who appeared to be finishing the game stronger.
In the 81st minute Brady sent Dargo racing clear through on goal but Cerny brought the Saints striker crashing to the ground just outside the box to pick up a deserved red card.
Substitute goalkeeper Sean Murdoch came on for McCarthy, while Dargo hobbled off to be replaced by Dennis Wyness but there was little more incident as the game ended as fragmented as it had started.