Partick Thistle scored two late goals to overturn St Mirren's lead and leave the Paisley side without a win this season.
An Aaron Muirhead clearance prevented a debut goal for Buddies forward Stephane Bahoken early on.
Kenny McLean tucked away the hosts' opener just after John Baird had missed an excellent chance for Thistle.
But Kallum Higginbotham levelled the match with a superb curling shot before sub Ross Forbes lashed home the winner.
The Jags claim a second win in the Scottish Premiership, while the home side have only one point from four matches.
St Mirren manager Danny Lennon insisted before kick-off he was not under any additional pressure, with the Buddies' defence of the Scottish League Cup ending at the first hurdle with defeat by Queen of the South in midweek.
And the Paisley side were almost gifted the lead when Bahoken, who has joined on loan from Nice, robbed the hesitant Jags defence.
The Frenchman nudged the ball beyond advancing goalkeeper Scott Fox only for Muirhead's outstretched foot to scoop the shot over.
There was another anxious moment for the visiting defence when Bahoken tried to convert off a Steven Thompson header, with a combination of Conrad Balatoni and Fox getting the ball clear.
The Jags asserted themselves towards half-time and James Craigen headed over before Steven Lawless flashed a shot just wide of David Cornell's goal.
Baird should have fired the visitors ahead at the start of the second half. The former Dundee forward latched onto a wayward pass-back and had only the goalkeeper to beat as he swept the ball wide.
Within moments, St Mirren were ahead as David van Zanten's low cross was turned in by McLean in the box.
Thistle were determined in their response and Stuart Bannigan had a shot blocked during one of several frantic moments in the St Mirren box.
Craigen's controlled half-volley from 20 yards was superbly saved by Cornell and Baird's replacement, Kris Doolan, was also denied by the Buddies goalkeeper.
Cornell was finally beaten by Higginbotham's bending shot following Doolan's inviting lay-off on the right-hand edge of the box.
Doolan also had a hand in the decisive goal, teeing up Forbes for a clinical finish.
Forbes had come on for Isaac Osbourne when the visitors had been chasing a leveller and Lennon threw on recent signing Jake Caprice in the hope of stimulating a late rally from his side.
However, the hosts could not find an opening and the full-time whistle soon confirmed a third defeat inside eight days.