Grinding out the win through some sloppy wet weather conditions on the sodden Rugby Park pitch, WBHS managed to shut down Rosmini's chances of getting over the advantage line with their spirited forward pack.
Slipping over on defence as well as on attack, Rosmini's penalty count went sky high towards the end of the match which allowed WBHS to clear the ball out of their half and make the most of the extra possession and territory gain inside the dying minutes.
Bustling their way up field with various pick and go's and penalty kicks due to Rosmini's lapse in discipline, WBHS held on to make history and boost their confidence going into the showdown versus St Kentigern's on Saturday.
With plenty of ball being spilt due to the slippery conditions, WBHS held Rosmini off their line on multiple occasions in the last quarter by forcing errors and turnovers to remain ahead at the fulltime whistle.
WBHS will face St Kentigern's in this Saturday's Blues regional final. The winner of that decider will represent the Blues' region at next week's national Top 4 tournament in Rotorua.
"I'm so proud that we've beaten the North Harbour champs, so we're looking forward to Saturday," Kapa said.
"We know it's going to be a really tough ask because it's going to be hard and fast down there. We now need to have a look ahead and see how they play but we know that they'll be big and physical and we'll just go as hard as we can."
WBHS play St Kentigern's on Saturday at 2.45pm and the match will be screened live on SKY's Rugby Channel.