Their tries were scored through 2023 Waikato flanker Joe Johnston and outside backs Cody Vai and Emoni Narawa.
Bay of Plenty pivot Kaleb Trask converted two out of the three tries and added a penalty right on halftime as they led 22-7 at the break.
Early in the second half, Johnston completed his brace to extend the visitors’ lead to 22 points.
Midway through the second half, Waikato burst through the Steamers’ defence with lock Lachlan McWhannell scoring and cutting into Bay of Plenty’s lead.
Reserve No. 10 Taha Kemara added the extras to make it a 15-point game with 17 minutes remaining.
However, the Steamers struck right back through midfielder Seamus Bardoul only five minutes later.
Trask added the conversion, to lead 36-14 with 12 minutes remaining.
Waikato fullback Josh Moorby scored on his homecoming debut as full-time approached.
After a mistake from Waikato at halfway, Kemara toed the ball through and it bounced up for him to grab and offload to Moorby in support who raced away to score.
Kemara added the extras to bring Waikato’s score to 21 but it was too late as the Steamers handed Waikato the defeat.
Other Waikato debutants in Saturday’s match were Hautapu’s Andrew Smith and University forwards Manaaki Boyle-Tiatia and Oli Mathis.
Waikato 21 (Quinn Tupaea, Lachlan McWhannell, Josh Moorby tries; D’Angelo Leuila 1 conversion, Taha Kemara 2 conversions)
Bay of Plenty Steamers 36 (Joe Johnston 2, Cody Vai, Emoni Narawa, Seamus Bardoul tries; Kaleb Trask 4 conversions, 1 penalty)
Halftime: 7-22