In an incredible match, where the lead changed hands seven times, the Blueheelers held their nerve and took the first step to healing the scars of last year's grand final loss to the Waratahs.

The Blueheelers will now face the winner of this weekend's Waratah-Tigers and Yanco-Wamoon preliminary final in the title decider.

If successful, the Blueheelers will become the first Yenda side in history to finish a season undefeated and the first Group 20 side to do it since Leeton in 1981.

But Yenda coach Andrew Lavaka said breaking records was the last thing on his side's mind.

"We don't look at the undefeated thing, we're just focused on winning each game as it comes," Lavaka said.

"We've had that attitude all year and that's why we've done so well."

In a see-sawing affair, the Waratahs led 12-10 at half-time.

Yenda came storming back straight after the break, with tries to brothers Trevor and Chris Richards within the first 10 minutes.

But the Tahs hit back with two of their own, the second to Ricardo Davis ? one of the tries of the season ? putting them 24-20 ahead.

Undaunted, Yenda struck back again with three rapid-fire tries and with just six minutes left, were 38-24 ahead.

Remarkably, the Waratahs had one last kick and tries to fullback George Broome and star centre Josh Charles slashed the margin to two.

It set the stage for a thrilling last three minutes but, much to the delight of the home crowd, some desperate defence from Yenda saved the day.

A bitterly disappointed Waratahs coach, Mark Palmer, said a possession drought in the second half had soured his side's chances.

"We had only 12 sets in that second half where we'd normally have 20," Palmer said.

"They just got all the possession and all the penalties and having to do so much defence really told on us.

"We'll just have to regroup now and focus on beating Yanco."

Best players for the Waratah-Tigers were Kose Leilei, Graham Levu and Josh Charles while Yenda's best were Chris and Steven Richards.