Tony Watt scored a dramatic last-minute winner to take all three points from Paisley.
The striker’s last-minute header ended the Steelmen’s run of three defeats, inflicting St Mirren’s third home defeat of the season.
Stuart Kettlewell made two changes to the side that lost to Dundee midweek, with Shane Blaney and Andy Halliday returning to the eleven as Kofi Balmer and Harry Paton dropped out.
Chances in the first half were few and far between as the wind in Paisley played havoc. Greg Kiltie had the best of the chances as he came in off the right and saw his effort crash off the woodwork. It looked like Aston Oxborough had made the decisive save, but the referee awarded a goal kick.
Shooting into the wind in the second half, the Steelmen made a better stab of it.
A clever interchange of play between Steve Seddon and Andy Halliday set the full-back free in the box, but his volley was superbly parried onto the bar by Balcombe in the St Mirren goal.
Tony Watt started to threaten his former side, with his skilful hooked ball enabling strike partner Apostolos Stamatelopoulos to bear down on goal, but despite an initially heavy first touch, he still managed to force a brave stop from Balcombe.
With time ticking away, Motherwell were firmly in the ascendency, and their efforts were rewarded with seconds to go.
Second-half substitute Moses Ebiye was impeded at the edge of the box—a foul that earned Alex Gogic his second yellow of the game and subsequently a red card. Skipper Lennon Miller stepped up and curled a magnificent delivery into the Saints six-yard box.
A silence overcame the stadium, followed by carnage in the away end, as Tony Watt expertly escaped his marker to nod home a vital first goal in claret and amber since returning to the club for his second spell.
It proved to be the last act of the game, with the three points propelling Motherwell back into fifth, two points shy of fourth-placed Dundee United, with the aforementioned heading to Fir Park next weekend.