Champions and favourites Cornwall were trailing Simon Lane’s Gloucestershire side 27-26 going into the dying seconds.
But with time up, Plymouth Albion hooker Rupert Freestone managed to get the ball down under the posts from a driving maul to give his side a 33-27 victory in front of nearly 2,000 people.
Freestone’s Albion team-mate Sam Matavesi had earlier scored two tries, with Matt Shepherd kicking three penalties and two conversions. Cornwall’s other try was scored by former Albion trialist Greg Goodfellow, who had come on as a replacement.
Duchy coach Dawe, who has guided the county to two successive Twickenham finals, said: “We had a wonderful crowd down at Redruth. It was a sea of black and gold and they really made a difference. Even Gloucestershire thought they got us over the line.”
Cornwall included seven Albion players in their starting line-up – Jake Murphy, Jon Dawe, Robin Wedlake, Shepherd, Freestone, Matavesi and Herbie Stupple. It should have been eight, but fly-half Billy Searle had to drop out on the day due to illness.
The Duchy had been 11-7 up at half-time but then went 20-11 down before coming back and taking a 26-20 lead only to then lose the advantage again.
“We won it then lost it again, before winning it again,” said a relieved Dawe.
“I think everyone apart from the players thought the game was over when we knocked on close to the try line, but from the scrum they (Gloucestershire) gave us a cheap line-out and we drove first, then picked and went before setting up another drive. We had a penalty but scored under the posts.”
Gloucestershire were always going to know all about Cornwall’s game as Lane had spent the season working with Dawe at Albion.
Dawe said: “We did not apply ourselves well enough in the first half, but Gloucestershire were quite superb in some of their plays. They played really well and forced us into errors. That was a credit to their line speed and tackling. They also have a very good back field and also drove well. They had a game almost to beat us.”
He added: “But we were delighted with our performance in the second half and it was great to get the win which we looked in danger of not achieving with three minutes to go.”
Cornwall may have reached Twickenham two years in a row, but Dawe is not getting carried away.
“You can win your first game and still get relegated,” he said. “And you can lose your first match and still reach the final.
“We’ve just got to grow and develop as a team over the next few days before going to Hertfordshire next week.”