Match ends, St. Mirren 3, Morton 1.
Lawrence Shankland's spectacular effort helped St Mirren to secure victory against their Renfrewshire rivals.
Shankland fired the hosts in front with his 10th goal of the season before Denny Johnstone restored parity just before the hour mark.
St Mirren restored their lead soon after when Callum Gallagher beat goalkeeper Derek Gaston.
Saints added to their lead in injury time as Shankland combined with Cooper to set up Stevie Mallan.
The victory takes Saints to within a point of Morton and boosts Alex Rae's side's chances of finishing fifth in the table with matches against Dumbarton and Rangers to come.
Morton, without a league win against their Renfrewshire rivals since 1999, were desperate to put that to rights as they come to the end of a season which had already ensured Championship survival.
The appeal of the fixture, meaningless outwith the possibility of Morton reaching a points total which would make them uncatchable by St Mirren, was clear with a crowd of 4,299 inside the Paisley 2021 Stadium.
Shankland scored a marvellous opener after just seven minutes, a strike from the edge of the box which flew beyond the despairing dive of Gaston.
The goal locked Saints' grip on the first half. Clarkson, back in the starting line-up, had a chance that he pulled wide. Gallagher shot past the other post - the goalie's left - and Mallan had a free kick saved.
Against all that, St Mirren keeper Jamie Langfield had a relaxing first half in the Paisley sunshine, save for a foot he had to use in an improvised save to deal with a shot from Declan McManus.
At first there was little redirection of traffic after the break despite Morton having spells of good passing. Bobby Barr, for example, was reluctant to release a shot and found himself forced wide to the by-line where his cross was blocked.
The Greenock side lacked a cutting edge but with 59 minutes they sorted that in grand style.
They launched a wonderful counter attack with Declan McManus doing the graft. Johnstone peeled off to his left and into space and McManus delivered the pass. Johnstone composed himself and produced a lovely finish.
However, within two minutes Saints were ahead again. It was sloppy defending by Morton captain Lee Kilday as his clearance landed at the feet of Gallagher who all but passed the ball in at Gaston's left post with a composed finish.
Saints decided to stick with what they had. With 14 minutes to go they replaced Gallagher with Jim Goodwin who took up a sitting role in front of the back four to nurse his team over the line.
St Mirren enhanced the victory with another goal in time added on. Morton were torn apart by Shankland and Cooper who set up Mallan to score. Job done.
Three points which saw them leapfrog Queen of the South and into sixth place in the Championship.
- 2NaismithBooked at 81mins
- 22GallagherSubstituted forGoodwinat 78'minutes
- 27QuinnSubstituted forCarswellat 82'minutes
- 24ClarksonSubstituted forMorganat 55'minutes
- 2KildayBooked at 52minsSubstituted forMcMullanat 65'minutes
- 7McKeeBooked at 60minsSubstituted forSamuelat 80'minutes
- 21McManusBooked at 86mins
- William Collum
- Shots on Target
Second Half ends, St. Mirren 3, Morton 1.
Goal! St. Mirren 3, Morton 1. Stephen Mallan (St. Mirren) right footed shot from the centre of the box to the centre of the goal. Assisted by Alex Cooper.
Corner, St. Mirren. Conceded by Declan McManus.
Declan McManus (Morton) is shown the yellow card.
Corner, St. Mirren. Conceded by Luca Gasparotto.
Substitution, St. Mirren. Stuart Carswell replaces Rocco Quinn.
Attempt blocked. Denny Johnstone (Morton) header from the centre of the box is blocked.
Jason Naismith (St. Mirren) is shown the yellow card for a bad foul.
Foul by Jason Naismith (St. Mirren).
Paul McMullan (Morton) wins a free kick in the defensive half.
Substitution, Morton. Alex Samuel replaces Joe McKee.
Attempt missed. Rocco Quinn (St. Mirren) left footed shot from outside the box misses to the right.
Substitution, St. Mirren. Jim Goodwin replaces Calum Gallagher.
Attempt missed. Joe McKee (Morton) right footed shot from outside the box is close, but misses to the left.
Attempt saved. Alex Cooper (St. Mirren) left footed shot from outside the box is saved in the top centre of the goal.
Alex Cooper (St. Mirren) wins a free kick in the attacking half.
Foul by Ross Forbes (Morton).
Attempt missed. Stephen Mallan (St. Mirren) right footed shot from outside the box is just a bit too high.
Gary Irvine (St. Mirren) wins a free kick on the right wing.