Middle-order batsman Kyran Dill was the only one to show any kind of resistance, scoring 41 before he managed to find a fielder trying to put away an innocuous delivery from Onerahi leg spinner Will Potter.
Kaipara finished on 114 all out from 45 overs with Onerahi's Tom Herman the chief destroyer with four wickets from his 10 overs, conceding just 23 runs.
The thick heat at Kensington must have taken its toll as Onerahi started just as poorly, losing three wickets within the first seven overs.
Kaipara would have thought themselves in with a shout after they took two wickets in the 17th over with the score at 42/5.
However, step up Onerahi gloveman Gabe Field, who was able to remain solid in defence and lead his team to a three-wicket win in the 41st over with an unbeaten 39 off 108 balls. Kaipara's Kyran Dill took four wickets in what was a losing battle.
Kamo ran through WBHS' defences at Kamo Recreation Ground as they had the schoolboys at 5/4 after just five overs and were all out for 76.
Boys' High batsman Chamodh Peiris was the top scorer with 32 but after he was dismissed the final five wickets fell for four runs to complete the victory.
If Kamo thought chasing the small target was going to be easy, they were rudely awakened when opener Lewis Miller was out first ball, caught behind off the bowling of Kurt Oldridge.
Despite Vincent van Mulert-Carvell taking three further wickets, Kamo chased down WBHS' total in 16.4 overs, earning them a bonus point for completing the chase in under 40 overs, and putting them into the final.
City were the ones to spoil Maungakaramea's party at the Maungakaramea Domain, chasing down the host's score of 151. City wicketkeeper Callum Garden scored an unbeaten 59 to give the visitors a five-wicket win in 33 overs.
Premier cricket now turns to the two-day competition next weekend, where Kensington Park will play host to both Maungakaramea against Onerahi and WBHS against City. Kaipara will take on Kamo at Bourne Dean Domain.