Porthcawl were 27-5 up thanks to Jordan Fox’s stunning first-half hat-trick and for large parts of the game Hynda’s team looked certain winners.
But Pembroke came roaring back and took the lead midway through the second half for the first time.
A brace of tries from Sam Smith and efforts from Dom Colman, Dan Colley and Tom Lewis did the damage, but just when they looked like they’d lost the game, Porthcawl won it at the death.
Pembroke were penalised for a high tackle and nerveless fly-half Josh White stepped up to slot the penalty and send those of a green and black persuasion wild with delight.
Hynda said: “What a game that was, I’m still speechless at what happened!
“I thought Pembroke had pipped us right at the end, but winning like that sums up our season and it’s just incredible. We have lots of belief, drive, and we always knew we were going to make it hard for Pembroke to win.
“We had world-class support throughout the game and that kept us going. We were in the ascendency for most of the game and our strength is in running the ball out wide and we had some joy in that area.
“But Pembroke did superbly to come back and we didn’t see it being that close when we were 27-5 up.
“Fortunately we stuck to our guns and we had a lot of confidence in Josh because he’s a big time player.”
Porthcawl produced some scintillating rugby to leave the home of Welsh rugby with victory.
“My heart was in my mouth at the end and there were definitely a few nerves there, but I think we put some of the professional boys to shame with the entertainment we put on out there,” said Hynda.
“We chucked it about and that’s what club rugby is all about. I’m so proud of the boys for pulling it out of the bag and this is something special.
“It’s absolutely huge for us and to see the club from where it is now is amazing considering where it has been in the past few years.
“We are so proud of everyone involved and hopefully this will put us on the path to more success. Porthcawl is a hot bed of sporting talent and I’m sure this will only nurture that.”
