Hastings Boys High School guard Harris Solomon shot well in the early stages and his consecutive three-pointers in the second quarter opened up Waikato's zonal defence to allow the bigs to dominate.
Dean Lautele guarded NBL player Dyson King with aplomb, contributing eight points in the third quarter when scoring had slowed.
The Bay will play the Mariners Tauranga who beat Gisborne Rising Suns 98-92 in the other semifinal on Saturday.
The final will be at Tauranga this Saturday with the time and venue details to be confirmed.
Result: HB 84 (M Wilson 25, W Dickson 18, A Daly 15, Harris Solomon 10, D Lautele 8) Waikato Pistons 74 (D King 21, K Rangiawha 17, J Harris 15).