Motherwell were not only unhappy about what they felt was a soft free-kick award, but that the ball was still rolling when Alex Gogic fired it out to the left prior to John winning the set-piece.
Nevertheless, the Fir Park side moved on from their angst, spending even more time in St Mirren’s defensive third as Apostles Stamtelopoulos lasered a low shot from the edge of the box which made Shamal George work.
But just as Motherwell looked to be on top, St Mirren produced a sucker punch.
Fresh from his outrageous overhead kick against Hearts on Wednesday, former Southampton and Bolton forward Nlundulu showed he can score beauties from distance too, unleashing a right-footed shot which arrowed into the right corner.
Mandron nearly made the most of a Motherwell mix-up to score again, only to be denied by a post, and Killian Phillips might have had his sixth of the season if he’d been more accurate.
For a few minutes near the end, extra-time seemed a possibility as Hendry pulled a goal back for Motherwell by sweeping in Tom Sparrow’s low centre.
But Jamaica international King replied almost immediately, his shot being blocked by goalkeeper Calum Ward before spinning outrageously up and into the net.
Then Phillips’ brilliant strike off the crossbar fell to Mandron to curl home beautifully and seal St Mirren’s win.
