It was Diamond's turn to return to the field wearing a red bandage - McArdle having sported the look in the last two games after his own head knock against Hearts.
Chris Dagnall saw a long-range strike deflected inches wide of Conrad Logan's goal - and from the subsequent corner McArdle climbed highest at the near post and connected with a thumping close-range header.
The Mendoza Line is calling its new album, the double-disc 30 Year Low, its last, and singers Shannon McArdle and Timothy Bracy, once married, have called it quits.