St Mirren soared back into the Premiership top six after Curtis Main's clinical strike against his former club settled a hard-fought affair in Paisley.
The Buddies were hoping to stretch their unbeaten run at the SMiSA Stadium to an incredible 12 matches against the only side to beat them on home soil in the league this season.
And they raced into the lead when Main stung his old employers, tucking in Ryan Strain's pinpoint cross sweetly at the front post.
Marcus Fraser made a couple of timely interventions in the second half to deny the Steelmen an equaliser, with Saints keeper Trevor Carson also pulling off crucial stops from Max Johnston and Stuart McKinstry deep in injury time to keep the hosts in front.
St Mirren held firm to capitalise on Aberdeen's heavy defeat to Hibs and leapfrog the Dons into the top half of the table once again, with former Saints boss Jim Goodwin swiftly sacked after the 6-0 rout at Easter Road.
Versatile midfielder Alex Gogic came into the heart of the St Mirren defence in place of Joe Shaughnessy, who was missing with foot injury.
New Zealand international Alex Greive was given a chance to impress up front, replacing fellow striker Jonah Ayunga to partner Main. Playmaker Greg Kiltie meanwhile replaced suspended Keanu Baccus in midfield.
The Buddies started on the front foot in Paisley, with wing back Scott Tanser flashing a shot just wide from a promising position.
And after struggling to score against Motherwell and an inspired Liam Kelly in their opening game of the season, the home fans only had to wait 15 minutes to breach the visitors' defence this time around.
Full back Ryan Strain raced down the right wing before producing an inch-perfect cutback to find Main, who tucked clinically past Kelly to open the scoring.
Motherwell hoped they'd have a quick chance to level from the spot when VAR was called to check for a potential penalty. There was a collective sigh of relief around the SMiSA Stadium when referee John Beaton signalled the check was over.
The Buddies were looking slick in midfield, with Kiltie pulling the strings. He released Strain down the wing before he curled a cross in which Mark O'Hara tried to acrobatically fire goalwards. Ethan Erhahon eventually won a free-kick at the end of the move which Strain fired powerfully into the arms of Kelly.
A neat one-two between Erhahon and Main in midfield saw the former cleverly play Strain into space again down the flank. His cross eventually dropped to Tanser, who volleyed over the bar from the edge of the box.
The home side's performance was markedly improved from the previous weekend when they looked disjointed against Championship side Dundee in the Scottish Cup.
Motherwell on the other hand hardly posed a threat in the first half, with Trevor Carson a virtual spectator in the Paisley sunshine.
The Steelmen took just one minute of the second half to finally threaten the hosts' goal. An inswinging corner found Ricki Lamie, who rose highest to head just inches past Carson's left-hand post.
Charles Dunne popped up in an unfamiliar position on the left wing as the Buddies regained control. The centre back flashed a brilliant cross along the six-yard line, with Main and Greive both too far away to capitalise.
The home side almost played themselves into bother when Tanser's misplaced pass sent the Steelmen racing in on goal.
A fizzed cutback found Stuart McKinstry who looked set to unleash a strike before Fraser blocked in the nick of time to snuff out the danger.
Stephen Robinson gave striker Ayunga the last thirty minutes to try and add to his goal tally, with the powerful frontman replacing Greive.
He immediately drew a foul from Lamie on the right wing, with the defender going into referee Beaton's book.
Fraser, fresh from signing a contract extension earlier in the week, pulled off another key interception when Motherwell substitute Olly Crankshaw raced through on the counter attack. The Saints defender again killed the chance when his team-mates' needed him.
Ayunga thought he'd doubled the Buddies lead when he cut through the Motherwell defence with a clever turn. A last-ditch challenge from Callum Slattery saw his effort deflected wide for a corner.
The Steelmen looked certain to level when Ross Tierney burst past Strain on the left wing before finding Max Johnston unmarked in the box. His powerful first-time drive drew an excellent save from Carson, who jumped on the rebound ahead of Kevin van Veen to keep the Buddies in front.
There was a late blow for the Saints as Ayunga was forced off injured after being involved in a heavy challenge. Youngster Kieran Offord replaced him, having only recently returned to Paisley from his loan spell at Alloa Athletic.
Main passed up the chance to bag a brace late on as he dragged a shot narrowly wide.
Deep into six minutes of injury time Carson again came to his side's rescue, pulling off a phenomenal stop from McKinstry's fierce strike to keep all three points in Paisley.
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