Starring in the win was halfback Rixon Russell, who orchestrated three of the Lions' six tries.

Gerringong will be contesting their fifth grand final in six years when they meet Shellharbour in the premiership decider this Sunday at Collegians Sports Centre.

The Knights were shattered after the game, trying to work out what went wrong after methodically carving out a 14-0 lead in the opening 30 minutes with tries to captain Luke Muttdon and prop Vaughan Thistlethwaite and three goals to fullback Tom Atkins.

The Lions seemed slow and lethargic before fullback Joel Roberts sparked them into action with a converted try, cutting the margin to 14-6 at half-time.

Kiama's lead was sliced to four with Alec Brookes' try five minutes into the second half and the Knights were shell-shocked when the Lions forged ahead 16-14 a couple of minutes later with 17-year-old winger Reuben Garrick's converted try.

Kiama's hopes of their first grand final appearance in 17 years were slipping away when Peter Cronin crossed out wide for the Lions.

Russell set up Garrick's second try from a perfectly-weighted cross-kick and Roberts converted for a 26-14 lead.

Try as they did to get back in the contest, the Knights must've sensed their opportunity had slipped away.

The Lions added salt to the wounds with centre Jack Murchie's try on the final play of the game.

"We couldn't get in the game in the first 15 minutes of the second half and had to do too much tackling, and there might've been a bit of fatigue with the heat," Kiama co-coach Matt O'Brien said.

"We started well and we played well in patches, but we weren't good enough today. Gerringong are a class side and they made us pay.

"It's disappointing not to go through to next Sunday, but the club's got three sides playing and we'll be there supporting them."

The Lions have a couple of injury concerns, most notably a hamstring issue for captain Brad Davidson, who failed to get through the first half.

"I should be right next week. I just didn't want to push it," Davidson said.

Seemingly down and out as half-time approached against the Knights, the Lions drew on their famous fighting spirit to overpower the home team with a dominant second-half performance.

"I'm proud as punch of the boys," Davidson said.

"We showed a lot of character to come back after being down at half-time.

"Some of the young guys put their hands up today. They were outstanding.

"It's always great to be in another grand final, so we'll get to the training paddock this week and give it our best on Sunday."