St Mirren had all of the possession and chances in the first half as they bombarded Kasper Schmeichel in the Falkirk goal.
Kirk Broadfoot started an attack after just two minutes with a close-range header which went narrowly wide.
Stewart Kean followed up ten minutes later with another header that went just over the crossbar.
The visitors were denied a penalty midway through the first half when John Sutton went down in the box, but eight minutes before the break they were rewarded for their efforts when Sutton went down again and this time was awarded the spot-kick.
Kean immediately picked up the ball and sent Schmeichel the wrong way to score a vital goal for his side.
The Buddies continued to look dangerous in the second half with their defenders pushing up and utilising the full width of the pitch.
Kean came close to striking the first blow of the half for the visitors lashing a shot in on the turn, but Schmeichel got a fingertip to it and it went behind for a corner.
On 57 minutes Garry Brady scored what could turn out to be the most important goal of his career to put St Mirren 2-0 up. He got on the end of a pass from Broadfoot and smashed a shot into the net from 12 yards out.
Falkirk's task was made harder minutes later when Karl Dodd, in his first match since returning from injury, was shown a straight red card for a reckless challenge on John Potter.