He was proved correct in a huge way on Sunday as his Cowboys downed Nyngan and advanced to a grand final date with Dubbo CYMS.

No moment was as big as the final minutes of the first half when an incredible tackle from James Stanley stopped Nyngan powerhouse Justin Carney from a trademark barnstorming try from close range.

That halted the Tigers' momentum after they had come back from 12-0 down to trail by just two, and then Wellington worked the ball out of trouble before capitalising on a Nyngan forward pass and scoring via a brilliant Josh Griffiths effort right on the half-time siren to set-up an 18-10 lead.

They went on with the job in the second half and while the Tigers rallied late the Cowboys ran out 38-30 winners to secure passage through to a first decider since 2010.

"That's game changing," Toomey-White said of the final minutes of the first half.

"It's those little things we talk about in the game that dictate the final result.

"It was individual brilliance from James to hold Carney up that close given how strong he is and then Josh getting early ball and he's light on his feet."

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The Cowboys are now one win away from a first premiership since 1994 while Nyngan's wait for a maiden Group 11 title continues.

Tigers coach Justin Carney said his side couldn't get too disappointed after the loss as they were beaten by a better side and one that made far less errors.

The mistakes were a real factor early, as knock-ons and penalties allowed the Cowboys to skip out to a 12-0 lead inside 10 minutes following tries to Tristan Lumley and Aidan Ryan.

A double to the hard-running Jone Yacadrau, the second as he caught the Cowboys napping and reached a Josh Merritt grubber before it went into touch, got the Tigers back within range but the huge plays from Stanley and Griffiths gave the Cowboys all the momentum.

Wellington then scored three tries in the first 16 minutes of the second half to take complete control, Griffiths nabbing a second in that time, and while there was a flurry of tries in the final 10 minutes the Cowboys were never in any real danger.

"What a feeling," Toomey-White said at the final whistle.

"It's been a long time coming for us. We've been so close for so many years.

"We've been knocked out week three so it's great feeling to see the boys play the way we played today.

"Previously against these guys we've started slow and they'd scored a couple of tries and got a sniff but today we controlled the ball early and made them work and got points from there."

Griffiths, playing back in the centres due to the absence of Steve Gordon following his concussion a week prior, starred in the win but suffered a shin injury inside the final 20 minutes which will be a real concern for the Cowboys this week.

He was unable to finish the game, while Lumley also spent plenty of time on the bench after appearing to aggravate a shoulder injury which has seen him miss plenty of game time recently.

The injuries won't be hurting as much as the pain the Tigers are feeling, with the club's season ending on Sunday following losses to the Cowboys in reserve grade as well as first grade.

There was real hype around Carney's Tigers following their minor semi-final demotion of Forbes but he said his side could have no real arguments after bowing out.

"Today we just lacked everywhere and that's footy," he said.

"Every try (they scored) was massive for us as we lacked in all areas. They weren't lucky tries. They were just dominated our eagerness and I can't really say there was any lucky tries or anything.

"We were just outplayed."

Wellington will meet CYMS in both the first grade and reserve grade deciders while the Fishies will also play in the juniors and league tag grand finals.

The sides in green and white meet Forbes in both of those games.