It all added up to Auckland's first defeat from four games this season as the visitors broke an 18-year drought in commanding fashion.
Any command belonged entirely to Auckland in the opening exchanges. With Roger Tuivasa-Sheck finally making his debut for the province, the hosts began with a roar that the Steamers would eventually silence.
Tuivasa-Sheck had a hand in the first try, as AJ Lam capped a sharp attack, then almost scored a second of his own but knocked on when Auckland were threatening to strike from the subsequent kickoff.
The home side continued to make midfield bursts through Tuivasa-Sheck and Lam, but their clear danger was somewhat neutralised when Harry Plummer saw yellow for tripping Zane Kapeli to halt a potential break.
The extra man allowed the Steamers to finally gain a foothold in the match, and it was one they wouldn't relinquish.
Bay of Plenty at first ran into some solid resistance, as Auckland defended their line well and won a couple of breakdown penalties to keep their lead intact.
But while Auckland continued to show flashes of menace, with another good offload from Tuivasa-Sheck setting his side away on another promising counter attack, only one side would have been feeling happy heading to the sheds.
Inga Finau's try right before the break - sparked by halfback Jamie Dobie charging down opposite number Taufa Funaki - saw the hosts' lead trimmed to two at halftime and gave them a warning they wouldn't be able to heed.
Auckland began the second spell as if knowing they had to exert more control on proceedings, putting together some positive phase play. But the Steamers defended capably enough and developed a habit of earning key turnovers to halt their opponents' progress.
And the visitors soon seized a lead that only the most ardent of Auckland fans would have denied they deserved, turning down a shot at goal and being rewarded when Nigel Ah Wong finished a fine move.
Kaleb Trask struck a couple of penalties to extend his side's advantage and cap a strong individual game, with Salesi Rayasi collecting a consolation bonus point while doing nothing to stem the Steamers' delight.
In the day's other games, Otago withstood a fightback from winless Southland to seal a 37-32 derby victory in Invercargill, while two tries from Brad Weber and a storming second half lifted Hawke's Bay to a 43-17 win over Manawatū in Palmerston North.
Bay of Plenty 21 (Inga Finau, Nigel Ah Wong tries; Kaleb Trask 3 pens, con)
Auckland 17 (AJ Lam, Salesi Rayasi; Harry Plummer pen, con, Simon Hickey con)
Halftime: 8-10
