They found themselves 20-4 down, before a rousing second half comeback gave them the lead on the hour mark, only for Matty Russell’s late try to condemn them to defeat.
Tonga said: “It was gut wrenching, a big game and we probably let ourselves down a bit especially in the first half.
“We can’t make any excuses for our errors, the way we started was really poor. The momentum certainly went our way in the second half.
“I thought the boys really picked themselves up and competed.
“Unfortunately a couple of calls had to be looked at but that’s the way it goes – we can’t change it, we’re going to have to move forward and re-build for the next two games.”
They will need to win both of those games to have any chance of making it through to the last eight.