Without Kerrod White, Lake stumbled to 4-45, then lost another four wickets for 22 runs mid-innings, eventually scraping together 132 off 44.3 overs.

In sweltering conditions, Kookas had their own issues, falling from 2-59 to 6-74, before captain Paul Clarke steered them to victory with an unbeaten 36, passing the total with three wickets in hand.

"We nearly had to carry him off in the end, he worked that hard for it in the heat," bowler Josh Cuthbert said.

"The last 15 runs took forever to get there, but it's a huge win for the club, especially when we were missing a couple of key players as well. Lake have had the wood on us for a while and it's always a big rivalry, so hopefully this will give us a bit of belief we can play finals."

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First-change option Chris Leaudais did the damage with the ball for Kookas with 4-34 off 10 overs, ripping through the middle order.

It's Lake's fifth loss in four seasons, such has been their recent dominance.

The result kept Kookas in touch with Oak Flats and Shellharbour on the overall ladder, as the two-dayers begin next weekend.

But it also sent The Rail to the top of the standings on quotient, after they held on for a nervy triumph of their own against Kiama.

The Rail will now meet Lake Illawarra in the one-day decider on Sunday.

Kiama fought their way to 194 off 47 overs, after Liam Mackrell and Jaya Hartgerink combined for a 76-run partnership.

But the failure to see out their overs cost them in the end, as The Rail chased the runs down with two wickets and 5.2 overs remaining.

Stuart Tobin top scored with 39. In the other match, Alex Brown hit 102 in Shellharobur 127-run demolition of Albion Park.