Heading into the second half with a 2-1 lead, 14-year-old Havelock charger Meaghan Broad set the pace by winning the pick-up, and firing off the first of her consecutive goals within the first 35 seconds.
Havelock upped the pressure, and continuing to pick off goals, the game ending in a 6-2 win, with Greaves scoring a hat-trick.
The team were expected to be in regeneration this year having lost four senior and experienced Year 13 players at the end of 2019, including Edilson and Terri Morrison (both current women's World U21 players).
Hawkes Bay coach and chairperson for Canoe Polo Hawkes' Bay Kelly Hepburn and co coach Morrison rallied the girls with trainings throughout winter.
Hepburn said she was "ecstatic".
"The girls had come away from regionals feeling a little deflated after losing by a decent margin to the same team.
"However, lockdown happened straight away following regionals, and coming out of it they found a new drive.
They trained in our outdoor facility right through the peak of winter. They took the school league through July-September very seriously and they committed 120 per cent to training.
"They came back on the weekend with a completely fresh perspective, a drive like I don't think I have seen in a team for a long time, and as a really tight-knit bunch they made me extremely proud of all of the work they have put in the past five months."
The event hosted on Canoe Polo Hawkes Bay's home grounds had more than 40 school teams from both the North and South Island traveling to the Bay to compete.
The last time the shield was retained back to back was when Hepburn won the title playing with Napier Girls' High School back in 2003.
Both Ashlee Greaves (18) and Meaghan Broad (14) were named in the national tournament team.
