Gerringong will have to play sudden-death matches throughout the finals to defend their title after a surprise 14-6 road loss to Albion Park-Oak Flats on Sunday.
The Lions are expected to wrap up the season with a home win over last-placed Port Kembla this weekend, but the loss to the Park means they are destined to finish fourth.
Kiama accounted for Port 26-8 at home on Sunday and will collect a further two premiership points with this weekend's final-round bye. That will guarantee the Knights fifth spot, regardless of this weekend's results.
Nowra-Bomaderry are assured of third spot, while Warilla hold a two-point lead at the top of the table over Shellharbour.
Gerringong were missing a few regular players against the Eagles and couldn't play their usual fast-paced game on a rain-soaked Centenary Field.
Albion Park have had little to celebrate this season and were determined to make their final home game a joyous occasion.
"You look at the guys coming through at our club and there's a lot of young kids, and it's just a matter of them finding that consistency," Eagles co-coach Adam Bezzina said.
"They learn from that and you can see the enjoyment today. They can take a lot away from it."
The Eagles took a 4-0 lead through winger Blake Jones's try and stretched the margin to 10-0 when Matt Carroll converted five-eighth Chris Rowles's try.
As the rain got heavier, Gerringong finally opened their account with Adam Moore's 60th-minute try, but the Park responded with Carroll's try and continually denied the Lions over the closing 15 minutes.
Both teams had to endure deplorable conditions and handling errors were frequent.
"I haven't seen the old Croome Road like this for a while," Bezzina said.
"It just kept on coming down at certain points when they had the ball, so maybe the footy gods were finally looking after us for a change.
"Gerringong are a good side. They had a few guys out but the boys were up for the challenge.
"The enthusiasm was there today, and that's the key for us. When we turn up with some enthusiasm, that's when we seem to match it."
Shellharbour stayed on Warilla's heels with a 64-0 rout of Milton-Ulladulla at Ron Costello Oval.