Wests Tigers' maiden Toyota Cup premiership win was driven by a player rookie coach Todd Payten wanted to cut before the season started.

The Tigers, who lost the 2009 under-20s decider to Melbourne, thrashed Canberra 46-6 on Sunday in an eight-tries-to-one mauling spearheaded by five-eighth Matt Mulcahy.

The 19-year-old only earned the No.6 jersey for the first time in round 26, but starred throughout the finals before winning the Jack Gibson medal as best on ground in the grand final following his two-try and two-try assist performance.

Star winger Marika Koroibete and fullback Kurtis Rowe both crossed twice as well to deliver Payten an under-20s coaching premiership to go with his 2005 NRL triumph playing with the joint-venture club.

But it was Mulcahy who stunned the rookie coach the most this season.

"I was going to cut him at the end of pre-season," Payten revealed.

"He was very relaxed and I took it the wrong way. I thought he didn't give a s**t.

"He had to bide his time ... and took his opportunity when it came."

Canberra started stronger, crossing through skipper Mitchell Cornish in the eighth minute for a 6-0 lead, but after that it was all Tigers, who crossed twice in the following six minutes to claim a lead they would never let go.

Those two tries were both set up by Mulcahy, to fullback Rowe and winger David Nofoaluma, and gave the Tigers a 12-6 lead.

Then the explosive Koroibete gave the Tigers a 12-point advantage at halftime when he scored his first moments before the siren.

Nothing changed after the break with Mulcahy and Koroibete both scoring brilliant solo tries, the latter a special 60-metre effort that turned into a foot race with Raiders speedster Jonathon Reuben - a race Koroibete was never going to lose.

That broke Canberra's spirit before tries to Mosese Fotuaika, Mulcahy and Rowe padded out the scoreline.

Payten said he hadn't expected the score to blow out as it eventually did, but the feeling still didn't surpass the joy of winning a premiership as a player.

"It's more fun as a player. I think you dream of doing that your whole life," he said.

"(But) don't get me wrong, this is enjoyable."