AndyDorman and Steven Thomson each netted a brace as the Buddies sunk Celtic to banish the painful memories of Sunday's Co-operative Insurance Cup final defeat.
St Mirren were 2-0 ahead thanks to strikes from Graham Carey and AndyDorman before Michael Duberry headed in a scrambled goal for the Perth side on 79 minutes.
AndyDorman gave the home side the lead in the 17th minute after he picked up a through ball from Dennis Wyness and slotted under the body of Ryan Esson.
The game got off to a thrilling start as Mehmet forced home goalkeeper Graeme Smith into a second-minute save following a flowing move up the left flank involving AndyDorman and Dennis Wyness.