Bay of Plenty, favourites after beating Hauraki 60-10 and Waikato 28-16, struggled on defence, giving Coastline forwards Rowdy Walker and Bobby Toheriri-Vincent too much room to move. Toheriri-Vincent was rewarded for his efforts with a try.
Although Bay of Plenty hit back 10 minutes later through winger Troy Winters, Coastline grabbed their second try through Matty Godfrey.
Lucky Walker converted both tries to put his side ahead 12-4 with only 14 minutes on the clock.
However, Bay of Plenty shifted up a gear and hit back with two tries to Josiah Vaevae and Te Ua Keepa, with Winters managing to convert one of the tries to edge Coastline 14-12 at halftime.
It was all one-way traffic after the break, thanks to the hard running of prop Zarius Easthorpe-Stevens. The youngster was a colossus on the hit-up and the visitors struggled to cope with his brilliant off-loading.
His efforts, backed by the rest of the forwards, help set up Cooper's four tries as well as Keepa's second and one for Dayharn Haimona.
Winters converted three of the six tries in the second half to take his side to a 44-12 win over Coastline.
Although Cooper was pleased to score four tries he said they had come about from teamwork.
"I think it was a good team effort, the boys were just putting their heads down and running hard as."
Despite the success of playing Cooper at centre he was not sure it would be a permanent move.
"I don't know, I'm not too sure ... it was good working off the boys and just getting up there and supporting them."
The Bay of Plenty coach said he was impressed with how the team coped with the intensity of playing three matches in one day.
"It was a little bit of a war of attrition, we picked up a lot of injuries throughout the day," said Nahu. "But we picked a good squad, guys that could cover a lot of positions ..."
Scorers: Bay of Plenty 44 (Troy Winters, Josiah Vaevae, Te Ua Keepa 2, Ezekiel Cooper 4, Dayharn Haimona, tries; Troy Winters 4 cons) Coastline 12 (Bobby Toheriri-Vincent, Matty Godfrey, tries; Lucky Walker 2 cons) Halftime 14-12.