Parkes (4-18 from eight overs) came on to bowl leg-spin in the 20th over of the innings and his crucial breakthroughs against the OBR middle order included two return catches.
The middle order was where the OBR batting line-up was at its strongest, and the spell by Parkes went a long way to ending the contest.
HSOB captain Carl Shaw had said before the final that his side would have to beat the best to be the best and he reaffirmed that theme after the game.
'It's awesome to win a trophy,' he said. 'We had to beat the champions. It wasn't easy.'
On a pitch that seemed on the slow side, HSOB had to bat in workmanlike fashion for much of their innings.
OBR bowled tightly but put down chances in the field and HSOB were able to bat out their overs, with Scott Tallott (32), who survived a run-out scare, providing some late impetus.
Shaw said OBR medium-pacers Ian Loffler and Craig Christophers were difficult to get away.
Opening bowlers Jimmy Holden and Cody Andrews collected three wickets each.
'OBR were good sportsmen the whole way through,' Shaw said. 'They bowled really well. There were no easy runs out there.'
He was pleased his team stuck to their task.
'I was happy with the way everyone kept their heads up through the game.'
OBR captain Jonathan Purcell was proud of his team's effort in the field.
'It was real muggy out there. The effort was there 100 percent. We thought at the break we were just in front but we knew we had to bat the overs.
Purcell said the all-round performance from 19-year-old Parkes was key.
'He showed why he's rated so highly.'
Parkes, batting at No.4, led a recovery effort with opening batsman Drew Scott (28) after HSOB were 13-2.
HSOB were still two wickets down at the 20-over drinks break and though they lost wickets regularly after that, their total looked about par.
In reply, OBR lost early wickets. They were 25-3 and then 70-4 when No.4 Andrews (26) was dismissed before the drinks break.
Loffler, batting at No.5, kept OBR in the hunt but their chances took a dive when he fell victim to Parkes for 30.
OBR went from 70-4 to 89-7 and Parkes had all of the first three wickets after the drinks break.
The top order left too much for the middle and lower order to do and they couldn't bring it home.
'Well done to HSOB. They were the better team,' Purcell said. 'We'll be back. I'm hoping that will fire the boys up for next year.'
The three teams in the A Grade will compete in the DJ Barry Cup competition after the Christmas break.