Royals qualified for the season decider with an absorbing win over the Queanbeyan Whites 33-30 on Saturday at Viking Park.

Four tries between wing duo Liam Slater and Seth Going lifted Royals to a thrilling win and earned them their first grand-final berth since 2002.

To win their first premiership since 1991 they'll have to beat a rampaging Tuggeranong, which is aiming for a title three-peat.

It's a task that doesn't faze the gutsy Royals, who overcame the loss of three starting players to beat Queanbeyan and withstood a Whites comeback in the dying minutes.

Royals coach Russell Ingram is confident his side can regroup and finally break Tuggeranong's dominance.

Tuggeranong has played in the past four grand finals and won three. ''We overcame adversity, a squad wins you a premiership and today that showed, this is a courageous group of guys,'' Ingram said.

''In three games against Tuggeranong there's been about one point between us, it's going to be a tight one.''

Royals will be without Australian sevens player and Olympic Games hopeful Tom Cusack.

Cusack ruptured his anterior cruciate ligament in the semi-final and faces up to 10 months on the sideline as he decides whether to have a traditional reconstruction or the revolutionary LARS surgery.

Cusack had impressed the Australian sevens coaches and was aiming for selection at the Games in Rio in 2016 when the rugby format makes its Olympic debut.

While Royals were riding high, the Whites were left shattered after they handed over a half-time lead and cost themselves a place in the grand final.

Had Queanbeyan won, the club would have fielded teams in every grand final next weekend.

The Whites were privately fuming with some controversial refereeing decisions.

Royals stole the ascendancy after half-time and took the lead with 28 minutes left in the match.

Slater scored his second try seven seconds after ACT Brumbies and Whites playmaker Robbie Coleman was sent to the bin and then Going scored his second to seal the result.

Queanbeyan No.8 Tom Darmody scored a try with time running out to give his team hope, but in the end coach Adam Fahey said poor execution cost the Whites.

''We lacked the composure and patience we've shown in the last month that wins you big games,'' Fahey said.

''The occasion got to us a little bit and we didn't execute as well as we should have. Credit to Royals, they responded to semi-final pressure better than we did. It does hurt to get so far and fall so short.''

ROYALS 33 (L Slater 2, S Going 2 tries; C McMahon 3 penalties, 2 conversions) bt QUEANBEYAN WHITES 30 (C Barbaro, L Freeth, T Darmody, D Penca tries; S Windsor 2 penalties, 2 conversions)

John I Dent Cup grand final: Saturday, Tuggeranong Vikings v Royals at Viking Park, 3.15pm.