They were also pulled back twice by the referee for forward passes with the tryline wide open.
"Down at halftime and a little dumbfounded, the boys were reminded we've been in this situation before, admittedly minus the noisy crowd," said Malcolm.
The decision was made to go to the bench as "war horse" Cade Robinson, big front rower Joey Veiogo and both the wingers were replaced, with Keanu Kaa, Shaquille Mckay, Keila Te Awhe and Villimoni Koroi introduced to up the tempo.
Koroi had immediate impact as he chipped ahead and headed off the PNBHS chasers to score out wide after five minutes.
First-five Sam Malcolm added a penalty butyielded an intercept try as the Manawatu team regained their momentum.
WHS captain Scott Bowater toldhis boys it was now or never, and after a free kick brought them to the corner, he scored from the lineout drive to narrow the gap to 25-13.
PNBHS would gain the scrum feed but lost procession, as WHS halfback Rory Gudsell fired a pass to Jesse Tupohu who linked with Te Rau Wirihana to get the converted try, 25-20.
With time nearly up a tired PNBHS put the kickoff out on the full. From the scrum, WHS held the ball to drag the defence to the right, then the backline attacked the left to put Te Awhe over in the corner.
Sam Malcolm's sideline conversion brushed the posts but having scored four tries to three, WHS were handed the trophy.
Darryl Malcolm said No 8 Sam Adams and lock Danyon Barr also deserved mention for big games.