American Jake Riddle talked his way into the bin for the Rays for 10 minutes shortly after the goal but while he was sitting out the penalty Steve Slonina was in the right place to redirect Kostadine's shot into the Panthers net for the final goal of the game after 23 minutes.
They could not cross the visitors' line but a third Lamb penalty, with Munster's Tuitupou in the sin bin for a spear tackle on Stringer, followed by a short-range drop-goal, gave the hosts a 12-3 lead.