The visitors built an early 10-2 lead as the hosts struggled to get into their offensive sets.
Again, it was the intensity on the defensive side of the ball that proved decisive - the Mariners turned up the pressure at the end of the first quarter and their fellow finalists could not live with them.
In a flash the score had gone from 16-16 to 34-22 - guard Ashton McQueen especially getting hot in a devastating period in which the Mariners essentially put the game away.
Aiden Daly and Dean Lautele toiled hard for Hawke's Bay, but ultimately could not overcome a deep, balanced attack that sprung occasional role players Adam Dunstan and Jonathan Dishroon as featured scorers in a number of sets.
McQueen, who looks likely to be heading down to play for the Otago Nuggets ahead of the next national league campaign, had a quiet second half on his way to a game-high 33.
"It was a bit dodgy towards the end and a bit shaky but good to get a win - we'll take it," McQueen said.
He was pleased to have been part of the team that took out the title and was looking forward to bigger and better things for the league. "It's pretty good for the first year but it definitely needs to get bigger. Five teams is not that great, but for the first year at least there are teams in it and we've got something to do."
Tauranga City Basketball general manager Mark Rogers congratulated all teams for taking part.
Tauranga City Mariners 89 (Ashton McQueen 33, Jonathan Dishroon 24, Adam Dunstan 13) Hawkes's Bay 73 (Aiden Daly 20, Dean Lautele 16).