The Buddies extended their impressive unbeaten home run to double figures after battling to a point against Hearts.
St Mirren raced into an early lead when Ryan Strain's powerful free-kick nestled in the bottom corner, aided by a deflection off the defensive wall.
The home side dominated the first 45 and should have added to the lead before the break, with Alex Greive spurning two excellent chances and Curtis Main also going close.
The Jambos made the Saints pay for their profligacy when Robert Snodgrass' wicked cross deceived everyone and tucked into the side netting shortly after the restart.
Curtis Main and Greg Kiltie both had opportunities to bag the hosts all three points throughout a much more even second half.
But after Marcus Fraser picked up a red card in injury-time for a reckless challenge, in the end the Buddies had to settle for a draw that stretched their superb unbeaten streak at the SMiSA Stadium to ten games ahead of a rematch with Hearts in Tynecastle on Friday night.
St Mirren had an early chance to break the deadlock after Keanu Baccus was barged down on the edge of the box by Cammy Devlin, following a misplaced Snodgrass pass that gifted away possession.
Strain stepped up to take the free-kick from 25 yards, with his powerful effort deflecting off Toby Sibbick in the wall before looping over a helpless Zander Clark and nestling into the bottom corner.
Prolific ex-Saints striker Lawrence Shankland was back on his old stomping ground and had his first sight on goal when he latched onto a Josh Ginnelly header. His near-post effort was well blocked.
There was an early blow for the Saints when goalscorer Strain went down after stretching to make a clearance. He hobbled off shortly after, with experienced head Ryan Flynn slotting into the same position.
The Buddies were in control of proceedings and almost doubled their lead when Mark O'Hara found Curtis Main in space on the left wing. He dragged a shot along the box that was just out of reach of strike partner Alex Greive.
Saints keeper Trevor Carson had been a virtual spectator but on the half hour mark he almost gifted the visitors an equaliser. His dreadful clearance scuffed along the ground before bouncing off Ginnelly, with the ball eventually going safe to spare his blushes.
Flynn was left raging at teammate Greive after the striker blocked his fierce volley that looked to be heading for the bottom corner.
Snodgrass whipped in a dangerous free-kick that Kye Rowles should have done better with at the far post as the off-colour Edinburgh side looked to fashion a leveller.
Baccus went into the book for going down too easily in the box under pressure from Alex Cochrane at the end of an excellent move.
Main fired over as the Buddies threatened to double their lead, with Greive following up with his own effort that cleared the bar.
The New Zealand striker had an even better opportunity just before the break when Main's cutback flashed across the six-yard box, with the ball just shooting underneath his feet as he tried to turn home.
St Mirren made a change at half-time as playmaker Greg Kiltie replaced Baccus, with the hosts picking up where they left off when Main's fierce shot was saved well by Clark at the near post.
Just four minutes into the second half Hearts levelled the scores. Snodgrass picked up the ball in space on the right wing before cutting inside Charles Dunne too easily and sending a whipped cross into the box. The dangerous ball beat everyone before nestling into the far corner past a stranded Carson.
O'Hara tried his best to replicate Strain's earlier free-kick and restore his side's lead when he blasted just wide with Clark beaten.
Alan Forrest, switched to the right side after the break, was looking much more of a threat for the visitors in the second half. He fired into the side netting from inside the box as the Jambos began to dominate proceedings.
Robbie Neilson's side should have taken the lead when Michael Smith raced to the byline before picking out Shankland unmarked in the box. The Scotland international couldn't get enough power on the header, with Carson comfortably saving.
Shaughnessy did well to stand up Ginnelly after he latched onto a Cochrane clearance, with the skipper using all his experience to snuff out the danger.
Shankland headed over again from a tough position as Hearts continued to press for a second.
Former West Ham midfielder Snodgrass again coughed up possession in the middle of the park, with Main driving a left foot effort that Clark beat away for a corner.
There was some late VAR drama with a check for violent conduct, with Marcus Fraser eventually sent off for placing a foot on Jorge Grant as he jumped to clear him at the start of extra-time.
Despite being a man down, the Buddies held on comfortably to pick up a point that kept their impressive home run intact.
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