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Marcus Fraser went into the book for a cynical foul on the left wing as United continued to impress early on.
Keanu Baccus tried to replicate Fletcher’s fine finish on the ten minute mark but skewed wide from distance as the Buddies tried to gain a foothold in the game.
The home side were still looking the more likely to find the net again and were inches away from doing just that when Aziz Behich’s superb effort sailed narrowly past the post with Carson scrambling.
Liam Smith was next to go close, slamming wastefully wide after a cross fell at his feet at the back post.
Greive, who netted at Tannadice last time around in August, tried his luck from distance but blasted well over the bar.
Loick Ayina slipped on the edge of the box to allow Curtis Main a strike on goal but his scuffed effort was comfortably held by Mark Birighitti.
St Mirren grew in confidence as the first half progressed, with O’Hara heading a dangerous Scott Tanser cross wide as they pressed for an equaliser.
United were always dangerous with Fletcher leading the line superbly.
The Scotland international was close to netting a second when he connected with a McGrath corner, with his deflected effort bouncing narrowly over the bar.
Robinson kept faith with the same eleven as the Saints returned for the second half looking to salvage something from the trip north.
The visitors were still struggling to create chances, with the first serious chance of note of the second half coming just before the hour mark.
Greg Kiltie did well to control a difficult ball on the right wing before pulling back to O’Hara.
United skipper Ryan Edwards pulled off a crucial clearance with the midfielder’s shot destined for the bottom corner.
Tanser’s cross from the left flank found Greive but the New Zealand international could only direct his header wide as the hosts clung on to their slender advantage.
St Mirren thought they’d levelled when Strain’s pinpoint free-kick picked out Taylor, who powered a header past Birighitti.
A lengthy VAR check ruled out his effort, but the Buddies didn’t have much longer to wait for an equaliser.
Loick Ayina clipped Main as he burst into the box, with the penalty confirmed after another long wait for the video officials.
O’Hara held his nerve, calmly sending Birighitti the wrong way to bring the scores level with just 15 minutes left on the clock.
Behich and Saints substitute Thierry Small missed similar chances to win it late on, with the former blasting over at back post before the latter fired wildly over the bar.
Small was making his presence known. The Southampton loanee burst past his marker before fizzing in a dangerous cross that evaded everyone.
The youngster was at it again shortly after but Main could only send a header wide from another promising pass.
St Mirren had eight minutes of stoppage time to try and find a dramatic late winner.
But it was the Terrors who spurned two excellent chances to claim all the points in stoppage time.
First Craig Sibbald saw an initial shot blocked with substitute Kai Fotheringham firing the rebound off the post.
Then Carson stood up magnificently to deny Mathew Cudjoe, producing a sublime one-handed save before Ilmari Niskanen fired over the rebound with the goal at his mercy.
The breathless second half still had one last chance up its sleeve, with Greive almost netting with the last kick of the game.
His dipping volley agonisingly cleared the bar, with the Buddies having to make do with a point.