The Demons found another level when it mattered, coming from 11 points down at three-quarter-time to down the Swans, 10.13 (73) to 8.12 (60) at Narrandera Sportsground.

Griffith's undefeated start to the season came to an end in their first final as the Swans struggled to reproduce their best football when it mattered.

They took an 11-point lead into three-quarter-time after kicking three goals in six minutes in a quarter that was otherwise dominated by the Demons, who could not convert.

Collingullie-GP started the fourth quarter with two goals inside the opening two minutes and kicked five of the six goals for the term to book their sixth grand final appearance in the past eight years.

Dereck Singe was the unlikely hero for the Demons, kicking three goals, two in the final term, to help the Demons to victory.

Marc Geppert also stood tall with two final quarter goals to finish with four in a match-winning display.

Collingullie-GP coach Luke Gestier never doubted his team for a minute.

"Their effort was fantastic and across the board, I couldn't fault them. It was fantastic," Gestier said.

"I kept saying to them, we've just got to stay in the contest. It's not as if I'm not backing them in, but we just had to stay in the contest, as long as we're in the contest, we're in the game.

"At three quarter time we were only 11 points down and we kept coming and coming and coming and eventually we got our nose in front. 

"I know we're a great last quarter side, even last year's grand final we kept coming and coming and coming, we lost it, but it's the fight in us that I just know these boys will keep giving. They're fantastic."

There was little between the two teams all day. 

The Demons led by three points at three-quarter-time, then worked hard to stick with Griffith in the second quarter, going into half-time two points down.

Collingullie-GP had all the play for the first 10 minutes of the third quarter but failed to capitalise before the Swans went up the other end and nailed three goals in six minutes.

The Demons' midfield got on top for most of the second half, working hard both ways as Collingullie-GP' defence proved rock solid and rebounded efficiently.

With a fortnight off before the grand final, the Demons now face a dilemma as to how many players they bring back for the decider.

Gestier, Jayden Klemke, Tim Beckmans and Joe Byrnes all expected to put their hand up to return from hamstring injuries.