Falkirk came from behind to sink the newly-promoted champions and confirm they will have no part to play in the relegation play-offs.
Jack Ross, the St Mirren manager, made eight changes after his side clinched promotion at the weekend, handing a debut to former Celtic and Hamilton midfielder Massimo Donati in a heavily-rotated starting line-up.
The Bairns came into the match on the back of two losses having also failed to score in their recent defeats.
There was little to enthuse either set of supporters in a lacklustre opening, devoid of attacking flair though Falkirk threatened first after seven minutes when Louis Longridge jinked past Donati before flashing a cross along the face of the goal, but no one added a finishing touch.
The visitors’ nerves were tested after 14 minutes but Gavin Reilly, chasing down a hopeful long ball, saw his effort from Bairns keeper Robbie Thomson’s clearance rebound over the bar.
Falkirk had the only shots on goal late in the first half when first Joe McKee blazed over the bar before Alex Jakubiak’s shot was easily held by Craig Samson. Jakubiak saw another effort blocked as the game came to life on the restart but it was Saints who made the breakthrough following a foul in the box by Paul Watson on Danny Mullen who was bearing down on goal.
Myles Hippolyte grabbed the ball and made no mistake as he smashed it high into the net.
Hippolyte may have had a second moments later but his effort from 12 yards was saved by Thomson who was then relieved when Mullen fired wide from a good position.
Saints clearly felt a second goal would seal the points and it almost came when Jack Baird’s downward header looked destined for the net until Bairns substitute keeper Conor Hazard produced a fine diving save.
At the other end Falkirk showed they were still in contention when Jakubiak fired inches wide.
The Bairns were handed the perfect opportunity to draw level as the match entered its closing stages when Baird mis-timed a tackle in the box and sent Watson tumbling to the turf. However, Lewis Kidd’s well-struck penalty was brilliantly saved by Samson diving low to the right-hand corner.
From the resulting corner Kevin O’Hara’s corner struck the bar but McKee followed up to score.
And Falkirk’s recovery was complete in stoppage time when Craig Sibbald was on hand to convert a cross from Jakubiak.