In the end a single penalty goal proved decisive in Kiama's gripping 8-6 triumph over long-time rivals Gerringong on Saturday at Michael Cronin Oval.

It was a classic old-school semi-final, a non-stop smash-up-derby that had both sides regularly questioning refereeing decisions.

Referee Craig Jones couldn't keep up with the pace in the second half, limping off with what appeared to be a hamstring injury and handing the whistle over to one of his touch judges for the final 15 minutes.

The Knights had to come from behind after trailing at half-time, booking a date with minor premiers Shellharbour in next Sunday's major semifinal at Ron Costello Oval.

"It was tough. We completed 50 per cent for the match, so we gave them a lot of ball and had to keep turning up," Kiama captain-coach Luke Muttdon said.

"To the boys credit they kept doing it."

A nil-all half-time score was on the cards before Knights fullback Tom Atkins broke the deadlock with a penalty goal.

But the Lions grabbed the upper hand with PJ Ford's try moments before the half-time siren sounded. Joel Roberts converted from out wide for a 6-2 lead.

Neither team was prepared to budge in the second half and the brutal hits - spiced with the odd cheap shot - just kept coming.

Kiama lock Josh Toohey managed to bust the defensive line in the 68th minute and ran 30 metres to score the game-trying try, while Atkins nailed the go-ahead conversion.

Gerringong centre Peter Cronin crossed the try line twice in the final 10 minutes but was denied by referee's calls on both occasions - once being held up and once for dropping the ball.

The Lions were adamant both should've been ruled fair tries.

"A few poor refereeing decisions turned the game a bit, but anyway, that's footy," Gerringong lock Brad Davidson said.

"They played really well and put pressure on us. It's disappointing to put in all that effort and still come away with a two-point loss."

While the Knights were mostly stifled in attack, they knew they could rely on their defence to get them home.

"We knew exactly what they wanted to do, they wanted to complete and build pressure, and we kind of just tried to out-Gerringong Gerringong," Muttdon said.

"We didn't really do it, but we just kept showing up.

"It'd been a while since we won down here at Gerringong, and to do it two times in a year is a real credit to the boys."

The Knights are on a mission to win the club's first premiership in 30 years.

"We've got a bit of confidence and we're riding high off a few wins," Muttdon continued.

"We beat Shellharbour a couple of weeks ago, and there's no reason why we can't do it again and set ourselves up for the grand final.

"It means a lot to the club and the town. That was the first final we've won in I couldn't tell you how long. A premiership would mean the world to a lot of people in Kiama.

"We keep saying it, that we haven't done anything yet. We've got two more wins two go and that's the focus. We'll go back to work next week and get ready for Shellharbour."