Hull had committed unnecessary numbers forward and were holding a worryingly high a line at the back when Mendy inexplicably missed a Ryan Shawcross punt upfield, allowing Ethrington to race in from the left and lash a powerful near-post finish past Matt Duke.
In between, Glasgow had almost stunned the home side after Sean Lamont intercepted a Jenkins pass on his own 22 and raced upfield, only for Aisea Havili to drag the wing down short of the Warriors line.