Head coach Clayton McMillan was delighted with the victory which gives his team the momentum of three straight victories going into the showdown in Wellington.
"We have always been really confident in the quality of our squad and today it was really tested. I am incredibly proud of how they fronted up and I feel we were in control of the match the whole 80 minutes," he said.
"I haven't said that much over the last couple of years so to do it on what was a pretty big occasion is really pleasing."
Otago opened the scoring with a penalty to Josh Ioane, quickly matched by Delany, before Webber showed his finishing ability to score in the corner.
Halfback Richard Judd injured his knee and was replaced after 21 minutes by Luke Campbell, who played a major part in the Steamers win in his blazer game.
Centre Foketi took advantage of a wayward Otago pass to run away to score by the posts. Delany converted for a handy 15-3 lead. But Bay dropped the kick off to give Otago their first period on attack which led to a try to hooker and captain Sam Anderson Heather.
Ioane kicked a penalty to close the gap to 15-11 before the Steamers finished the half with a crucial seven-pointer. Campbell made a sharp break before Chase Tiatia and Monty Ioane combined down Otago's right side to set up Foketi to crash over.
Bay of Plenty led 22-11 at the break but were set back immediately after the restart when openside flanker Hugh Blake was yellow carded in a tough call by referee Brendon Pickerill.
Otago scored immediately through No 8 Sione Teu but did not make the extra man pay for long as the Steamers came storming back on attack. Webber made another excellent run to finish in the corner.
Delany converted with a superb kick into the cross breeze.
Otago bombed a certain try with a dropped pass after Latu Vaeno broke through some weak tackles. It proved costly as soon after a text book lineout drive saw Henry Stowers driven over for a 34-18 lead.
But Otago came back after weak defence let in Vilimoni Koroi to score in the corner. Smith slotted the conversion from touch so it was game on at 34-25 with 16 minutes to play.
Then the decisive moment came as outstanding second five Terrence Hepetema dived over for a deserved try after a sustained period of pressure. Delany added the extras to stretch the lead to 41-25 with 11 to play.
Otago scored a late converted try but the Steamers looked assured in holding out over the final few minutes. As the siren sounded, they were awarded a penalty try to add some late drama and spark jubilant scenes among the 5,000 home supporters.
Bay of Plenty 48 (Joe Webber 2, Lalakai Foketi 2, Henry Stowers, Terrence Hepetema, penalty try tries; Mike Delany 5 cons, pen) Otago 32 (Sam Anderson-Heather, Sione Teu, Vilimoni Koroi, Teih Walden tries; Josh Ioane 2 pen; Fletcher Smith 3 con) Halftime: 22-11 Bay of Plenty
