Playing in front of a sizeable home crowd at Ocean Park, Shamrocks burst out of the gates to race to a 17-0 halftime lead.

They then held their nerve in the second to secure a tense 27-21 victory, with coach Paul Ridgway praising his team for digging in to secure the win.

"Overall I was happy with the first half, to be up 17-0 at halftime," Ridgway said. "With a pretty stiff wind, we needed that lead. Our first half was pretty impressive.

"But Vikings are a really good side, it was a physical encounter and Vikings teams don't ever give up. They would have come here today as part of our 50^th celebrations, it's a long rivalry and they came to play. They kept coming and they could have got away with it in the end there."

The two teams were evenly balanced throughout much of the match, with Vikings looking threatening when they held the ball for repeated phases. They struggled to build pressure, however, with numerous errors preventing the visitors from capitalising on their opportunities.

Despite the errors, Vikings came close to spoiling the party when they finally clicked into gear throughout the final 20 minutes. Converted tries in the 68^th and 78^th minutes cut the deficit to just six points.

Those two tries set up a grandstand finish, with Vikings having one last attempt to pull off the miracle comeback. Shamrocks held firm, however, to secure the victory.

"Our guys have an appetite for that physical part of the game. Their defensive structures are really good and they trust each other a lot.

"We talk a lot about not letting teams cross our line, that's the most points anyone's scored against us since round two when we played Avondale. It's a real strength of our game and that's a credit to Vikings, they played some really good footy."

Read more: Illawarriors out to defend title at NSW Country Rugby Union Championships

The victory capped a successful day for Shamrocks, with the club claiming victories in all three grades.

For Ridgway, the culture the club has built over 50 years shone through in each team's performance.

"It's a big day for the club. You don't have to look too far to see a lot of old faces around and that it means a lot to us.

"We're a club that's built on hard work and people chipping in and working together. We're really proud of the fact we're all juniors, we don't bring any people in and that's really important to us.

"We'll have a pretty good celebration tonight, three wins is pretty special."

While you're with us the Illawarra Mercury is offering sport readers 20% off an annual digital subscription. Sign up to stay up to date with all the local sports you love for only $3.00 a week. Terms and conditions apply.