Experience and know-how.

It was the key on Saturday as a well-drilled Forbes Platypi ground out a 22-19 bonus-point win over the Roos to leapfrog the Dubbo team and move into the Blowes Clothing Cup finals.

The Platypi, featuring a close-knit core group which led the club to a drought-breaking first grade title in 2017, showed the kind of desire and composure needed at this time of year.

In a gripping contest played at a finals-like intensity at a bouncing Grinsted Oval, back-to-back tries early in the second half and then a wholehearted defensive effort late in the contest saw the Platypi take out the winner-takes-all contest.

While the Hammond and Jarrod Hall-led Forbes side remained patient and calm in those final stages, the Roos appeared panicked at times with forced passes and errors destroying their chances of staying in the top four.

"There at the end, we knew we had to dig deep and the boys needed to step up," Forbes co-captain-coach Hammond said of the desire within his squad.

"That defence there at the end was absolutely incredible and if we can take that into the next couple of weeks of the finals we can give it a real shake."

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The sides finished level on 30 points but Forbes advanced having won one more game than the Roos' this season.

Forbes hadn't been in the top four for the past six weeks, but now head into the finals having won three of their past four games.

"It feels incredible. We set out to prove people wrong. We were predicted to come fifth and wouldn't be in the finals but we are now and it's a very good moment for the boys," Hammond added.

While many in the Central West rugby community may have expected the Roos to go on and finish in the top four after a clinical 57-17 win three weeks ago had the side eyeing third spot, losses in the two final rounds see them miss the finals for the second successive season.

"That sums up our season," Roos' director of coaching Robinson said.

"We were not quite with it and as I just said to the boys, in the end we didn't earn the right to be there even though we could have."

The Roos were dealt a blow before a ball had been kicked as both captain Shaun McHugh and star outside back Tim Beach were ruled out.

McHugh was out through illness, having not been able to go to work in the week leading up to the game, while an injury suffered in last week's loss to Cowra saw Beach miss out.

Robinson flat-out refused to use that as an excuse, but McHugh's leadership and calming influence was missed as much as Beach's explosiveness and ability to find the try-line.

Execution was an issue for Robinson's side at times, but he said inconsistency across the game and on and off the field this season as a whole was the biggest issue.

"You look at those Forbes boys and a lot of them have been playing together for a good few years and they're clicking," Robinson said.

"We've got to get that good foundation and play as much rugby together as we can, but also come together off the field.

"It's about making a conscious effort because you don't just win a competition on a Tuesday, Thursday, and Saturday. It's more than that."

The Roos began well but mercurial scrumhalf Mahe Fangupo soon started to get his hands on the ball more and was involved as the Platypi, wearing one-off old school charity day jerseys, scored the game's first try on nine minutes.

After getting through a number of phases, fullback Josh Coulthurst motored through a gap to score out wide.

The Roos, somewhat against the run of play, hit back 10 minutes later when a turnover led to Hamish Gordon streaking away down the short side to score and when his kick was waved away it was all square at 5-all.

But again the Platypi built pressure and kept their hands on the ball, using strength to work their way up the field and eventually across the line through burrowing NSW Country prop Charlie French.

With so much on the line for both sides tensions were simmering and the first half soon became dominated by stoppages where referee Nathan Pearce laid down the law to both sides.

Despite the Roos' building frustration, they got the all-important try before the break through Ned Williams and went into half-time with a two-point lead.

But the game changed in the first 10 minutes of the second half when two attacking raids down the right edge resulted in tries for Forbes' Simon Bayley and Isac Stuart.

Errors were creeping into the Roos games, one of the quick-fire tries coming immediately after a knock-on from the visitors, and while Anthony Golding finished off a slick attack to get his side back within range, the Roos never really created any clear-cut chances in the final stages.

Much of that was because of the Forbes defence, plus the home support which Hammond described as "awesome" during the club's annual charity day.

The Platypi now go on to meet the Cowra Eagles in the opening week of the finals.

"We've got Cowra and we're going to have a real red-hot crack," Hammond said.

The Roos, having previously not missed the finals since 2011, now haven't made the top four in back-to-back seasons.