Riordan had joined up with his team-mates only hours after flying to the Netherlands having been granted compassionate leave by manager John Hughes to attend the happy event on Thursday morning as the rest of the squad were preparing to depart.
The Scotland striker had started the match on the bench but when fellow substitute Anthony Stokes was felled 25 yards from goal there was no doubt as to what was about to happen, Riordan stepping up to curl the ball beyond NEC goalkeeper Gabor Babos, a goal reminiscent of his winner against Kilmarnock in March.