Kris Doolan headed in at the back post to give the home side the lead but Kenny McLean slotted home a penalty just before the break to draw Danny Lennon’s side level.
Both sides hit the frame of the goal in the second half but neither could fashion a winner.
The game took time to settle into a rhythm before Partick began to assert control and edge ahead, with Doolan looping a header over St Mirren keeper Chris Dilo and into the net after Kallum Higginbotham had crossed with the outside of his right boot.
A clumsy foul from Higginbotham on Jason Naismith then gave the away side a way back into the contest and McLean calmly converted the resulting spot-kick.
Leer Mair spurned the opportunity to take Partick back into the lead in the second half after directing his header into the turf and over the crossbar after Higginbotham had picked him out in the middle with a free-kick.
Higginbotham continued to cause problems for the away defence with a low cross from the right that substitute Christie Elliott just failed to convert.
That almost proved costly as St Mirren came into the contest in the closing stages, McLean smashing a shot against the post from the edge of the box.
Thistle goalkeeper Paul Gallacher was then forced to get down smartly to keep out a powerful Sean Kelly shot.
There was still time for one final chance as Partick sub Lyle Taylor saw his header beat Dilo only for the ball to come back off the crossbar, leaving the sides to settle for a point apiece.