Billy Mehmet's penalty sent St Mirren into the last four of the Scottish Cup at the expense of a toothless Celtic.
Saints almost opened the scoring within two minutes but Garry Brady was denied by a superb Artur Boruc save.
Celtic striker Scott McDonald's header was correctly chalked off for offside in a goalless and drab first half.
The hosts broke the deadlock when Stephen McManus was yellow carded for scything down Craig Dargo and Mehmet deservedly fired Saints through.
St Mirren started brightly as they looked to avenge last weekend's bruising 7-0 defeat when the two sides met on league duty at Celtic Park.
They were compact and tenacious in the tackle; giving the Celtic midfielders little time on the ball and ensuring McDonald and Jan Vennegoor of Hesselink got little joy in the opening 45 minutes.
Brady forced Boruc into punching clear within two minutes after the midfielder found himself clear on the right inside the 18-yard box.
Celtic almost took the lead with their first foray forward in the sixth minute when right-back Andreas Hinkel sent a wicked low cross into the area, but McDonald was unable to force the ball home at the back post.
The visitors had a goal chalked off in the 14th minute when McDonald was rightly flagged offside after he glanced home Shunsuke Nakamura's from close range.
Aiden McGeady danced past a couple of challenges before trying to thread the ball through to McDonald six minutes before the break, but the Saints defence was alive to the danger and the ball was cleared.
Dorman whipped the ball away from McDonald on the stroke of half-time after the Australian striker was played in by Nakamura.
The start to the second half was just as cagey as the first and Celtic defender Darren O'Dea had the first effort on goal in the second period when he headed over from Nakamura's corner.
But St Mirren shook the game to life after 54 minutes when they broke the deadlock in dramatic circumstances.
Dargo sprinted towards goal and McManus scythed down the striker just as he was about to pull the trigger.
The Celtic captain was shown a yellow card for the foul, with team-mate Gary Caldwell's tracking run saving McManus from a straight red.
Mehmet took the penalty and slotted the ball low to Boruc's left-hand corner to give the hosts the lead.
Saints's goal stung Celtic into action with McGeady and Nakamura looking to breach the home defence, but with little conviction.
Celtic's problems in front of goal were compounded when the out-of-sorts Vennegoor of Hesselink received a yellow card for handling in the box as he mistimed a diving header.
St Mirren almost doubled their lead after 73 minutes when Hinkel failed to deal with Brady's corner and Crosas blocked Dargo's shot before the ball was cleared.
Georgios Samaras was then introduced for the Spanish midfielder as Celtic looked to find an equaliser, but their attacks were too often ponderous and lethargic.
Dorman was denied by Boruc before Dargo spurned a chance to extend St Mirren's lead.
Vennegoor of Hesselink completed his and Celtic's miserable afternoon when he headed straight at goalkeeper Chris Smith from eight yards.
Saints held on to secure a place in the last four as Celtic bowed out at the quarter-final stages for the second year running.
Billy Mehmet's penalty sent St Mirren into the last four of the Scottish Cup at the expense of a toothless Celtic.
Saints almost opened the scoring within two minutes but Garry Brady was denied by a superb Artur Boruc save.
Celtic striker Scott McDonald's header was correctly chalked off for offside in a goalless and drab first half.
The hosts broke the deadlock when Stephen McManus was yellow carded for scything down Craig Dargo and Mehmet deservedly fired Saints through.
St Mirren started brightly as they looked to avenge last weekend's bruising 7-0 defeat when the two sides met on league duty at Celtic Park.
They were compact and tenacious in the tackle; giving the Celtic midfielders little time on the ball and ensuring McDonald and Jan Vennegoor of Hesselink got little joy in the opening 45 minutes.
Brady forced Boruc into punching clear within two minutes after the midfielder found himself clear on the right inside the 18-yard box.
Celtic almost took the lead with their first foray forward in the sixth minute when right-back Andreas Hinkel sent a wicked low cross into the area, but McDonald was unable to force the ball home at the back post.
The visitors had a goal chalked off in the 14th minute when McDonald was rightly flagged offside after he glanced home Shunsuke Nakamura's from close range.
Aiden McGeady danced past a couple of challenges before trying to thread the ball through to McDonald six minutes before the break, but the Saints defence was alive to the danger and the ball was cleared.
Dorman whipped the ball away from McDonald on the stroke of half-time after the Australian striker was played in by Nakamura.
The start to the second half was just as cagey as the first and Celtic defender Darren O'Dea had the first effort on goal in the second period when he headed over from Nakamura's corner.
But St Mirren shook the game to life after 54 minutes when they broke the deadlock in dramatic circumstances.
Dargo sprinted towards goal and McManus scythed down the striker just as he was about to pull the trigger.
The Celtic captain was shown a yellow card for the foul, with team-mate Gary Caldwell's tracking run saving McManus from a straight red.
Mehmet took the penalty and slotted the ball low to Boruc's left-hand corner to give the hosts the lead.
Saints's goal stung Celtic into action with McGeady and Nakamura looking to breach the home defence, but with little conviction.
Celtic's problems in front of goal were compounded when the out-of-sorts Vennegoor of Hesselink received a yellow card for handling in the box as he mistimed a diving header.
St Mirren almost doubled their lead after 73 minutes when Hinkel failed to deal with Brady's corner and Crosas blocked Dargo's shot before the ball was cleared.
Georgios Samaras was then introduced for the Spanish midfielder as Celtic looked to find an equaliser, but their attacks were too often ponderous and lethargic.
Dorman was denied by Boruc before Dargo spurned a chance to extend St Mirren's lead.
Vennegoor of Hesselink completed his and Celtic's miserable afternoon when he headed straight at goalkeeper Chris Smith from eight yards.
Saints held on to secure a place in the last four as Celtic bowed out at the quarter-final stages for the second year running.
