Goals from Billy Mehmet and Andy Dorman saw St Mirren leapfrog a lacklustre Falkirk at the bottom of the SPL.
The visitors from Paisley made a flying start, with Jack Ross twice going close from long range and Hugh Murray's header hitting the crossbar.
The impressive Mehmet raced away from the Falkirk defence to slip the ball into the net after 37 minutes.
Mehmet squared for Dorman to slide home on 73 minutes, while Falkirk's Steven Pressley was shown a late red card.
Backed by a large travelling support, the Buddies turned in a tremendous display to virtually assure their top flight status.
Only a heavy defeat at home to Hamilton, who are already safe, coupled with a Falkirk win at Inverness would see them drop back to the bottom spot on the final weekend.
Falkirk, who were simply awful, will need to radically improve against Inverness to have any hope of avoiding relegation.
A fired-up St Mirren completely dominated the first 45 minutes, with the hosts looking nervous and making all sorts of errors.
On seven minutes, Falkirk keeper Dani Mallo made a great fingertip save to keep out a stinging 22-yard drive from Jack Ross.
And, from the resulting corner, Buddies midfielder Hugh Murray sent a glancing header against the crossbar.
Gary Mason was next to try his luck with a curling effort and Mallo was far from convincing as he got down to scramble the deflected shot wide.
St Mirren midfielder Andy Dorman hammered a strike on target but Falkirk defender Tam Scobbie made a brave block and Ross then smashed a fizzing long-range shot against the junction of post and crossbar.
Mehmet flicked a dangerous Dorman free-kick narrowly wide before the latter created space for himself only to shoot high and wide from a promising position.
The deserved breakthrough came on 37 minutes when Murray intercepted a dreadful clearance from Pressley to nod the ball on to Mehmet from the halfway line.
The big striker easily outpaced the cumbersome Pressley and kept a cool head to slot the ball beyond Mallo.
Torrential rain and strong winds made for a scrappy opening to the second half but when the downfall abated the game burst back into life.
Mehmet squandered a great chance, heading straight into the arms of Mallo on 64 minutes and Steve Lovell broke free at the other end only to shoot against the legs of diving Buddies keeper Mark Howard.
Mallo got fingertips to an acrobatic overhead effort from Mehmet but the Buddies did not have long to wait for another goal.
Dorman knocked a clever ball over the top for Mehmet to run on to and the big striker held it up well before rolling it back for the midfielder to slide in and finish the move he had started from 10 yards out.
Pressley capped a day to forget for the home side when he was sent off on 88 minutes for crashing into Mehmet, while leading with an elbow.
Falkirk manager John Hughes: "St Mirren deserved to beat us. For 90 minutes they looked sharper, they looked hungrier.
"They looked like they wanted it that bit more and they played some good stuff as well.
"I can understand the tension but I'm disappointed in the performance of the team. We were a bit predictable and we didn't work their goalkeeper.
"We just need to regroup and go again next weekend.
"I'm trying to pass on 25 years of experience in the game and that's possibly the only thing that gets me exasperated.
"That was our cup final today and, if that's the reaction, boy, we're in trouble."
St Mirren manager Gus MacPherson: "We dominated from the very first whistle when a lot of people were expecting us just to turn up and be beaten.
"The players were very quiet after Wednesday's loss but I knew I'd get a reaction.
"Billy Mehmet gets criticism from our own support because he maybe doesn't score the goals you'd expect from a centre forward but there is so much more to his game.
"There are a lot of centre-backs that don't like playing against him and he certainly gives 100% every time he plays."
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