A field goal from Group 3 representative halfback Anthony Cowan in the second period of golden point sealed the deal for the Mustangs, but it could have been so different minutes earlier when Aaron Ison's effort from about 40 metres hit the crossbar and bounced out.

Ison's attempt didn't look to be going close, but grew legs in the last 20 metres. It had the Blues and Mustangs crowd on its feet.

An earlier Blues effort in the corner in front of the Mustangs crowd was disallowed.

Cowan had another shot earlier in extra time. He hit it well but it sailed agonisingly wide, much to the relief of Blues fans.

They were soon cruelled by his boot later in the contest.

A sizeable Stangs crowd invaded the field when referee Corey Richardson's whistle confirmed Cowan's attempt had gone through the posts.

It was a cracking grand final where neither team could be separated. The players were dead on their feet as the golden point time wound down.

Ison scored a try earlier which put his team ahead 24-18, but a Steve Walker try and Cowan conversion forced the game into extra time.

Earlier, the Blues were in front 14-10 but the Mustangs fought back to lead 18-14 at the break.

The Blues led early thanks to an unconverted try from Reuben Trick.

The Mustangs hit back with a couple of tries before Nick McCabe and Beau White found the line to give the Blues the ascendancy again.

Retiring Blues captain Robbie Trembath said it was the best grand final he'd ever played in.

He lamented missed opportunities in the loss.

"We always knew if we gave them opportunities, they'd take them, but we didn't take ours," Trembath said.

"I'm a little bit disappointed by some of our execution, but at the end of the day, it was a game of footy and just like the three other games we'd played them in this year, they've been good games."

He had plenty of good things to say about his team's effort all season.

"We probably lost four or five of our best players from last year, and only replaced them with a couple," Trembath said.

"I'm really proud of the team that we put on the paddock every week.

"For the boys who stepped up, the Kurt Dohertys and Chris Hudsons and those sorts of blokes, I couldn't be happier with them."

Mustangs captain Sam Howe was thrilled to win.

"That was unreal," he said.

"It was such a tough game, and that's how grand finals should be.

"I've got nothing. No words to say."