Vini picked up a try of his own but Mid Northern didn't allow the Sharks to get away as they scored two tries in fairly quick succession late in the first half.
The first one came via a brilliant cut-out ball from fullback Kiali Leuluai, who found No 8 Tepara Job for the try.
Mid Northern crossed for another through Job to give themselves a 19-10 lead going into the break.
Sharks came out of the break hungry led by Northland rep Matt Matich, playing at second five, and flanker Michael Frood.
But a try of a charged-down kick by Toby Parr put Mid Northern out to a 26-13 lead.
Sharks continued to hammer Mid Northern and found their way over the line as winger Hamish Stokes found space and scored to reduce the deficit to six with just minutes on the clock.
However Mid Northern stood tall on defence to hold them out and take the bonus point victory.
Sharks coach Mark Russell was fairly happy with his unit but they didn't take advantage of the strong breeze.
"I thought the boys defended well, we're pretty happy with that part of our game, but going into the second half we knew we had the wind but didn't utilise it well enough," Russell said.
"The boys know we aren't far away. We've been really happy with the effort in the last couple of weeks.
"We're always targeting the set piece for improvement. It's a crucial part of the game. Mid Northern and Old Boys Marist have the two best scrums in the competition so it was a great test for us.
"There's a whole eight or nine weeks before we face those sides again so it gives us something to aim at."
Meanwhile Kamo grabbed their third straight win as they pipped Mid Western 27-25.
Kamo were pushed to the limit but managed to grind out the victory.
OBM continued their unbeaten run with a 50-19 win over Hikurangi.
Hikurangi were boosted by the services of NZ Under 20 rep Tamati Tua playing at fullback.
However OBM played with a lot of pace and penetration with returning centre Troy Gilbert scything through the backline to score by the posts and promoted reserve grade player Raydin Smith putting in an impressive performance on the right wing.
The win didn't come without its challenges, however, with Matt Harrison and Micky Seymour both having 10 minutes in the bin.
Wellsford picked up an upset win over Hora Hora, comfortably winning 39-15.
The southern side had been struggling in recent weeks but found an attacking spark to take down their opponents.
The final match was an enthralling draw as Otamatea and Waipu battled to a 15-15 stalemate.
Results: Premier:
Mid Northern 26 Western Sharks 20
Kamo 27 Mid Western 25
OBM 50 Hikurangi 19
Otamatea 15 Waipu 15
Wellsford 39 Hora Hora 15
Premier Reserves:
Mid Northern 42 Western Sharks 0
Kamo 60 Mid Western 5
OBM 68 Hikurangi 7
Otamatea 36 Waipu 17
Hora Hora 24 Wellsford 22
North Zone:
Awanui 27 Kerikeri A 4
Eastern 53 Kaeo 22
Kaikohe 37 Kaitaia 15
Ohaeawai/ Okaihau 57 Te Rarawa 12
Kerikeri B 37 Panguru 14
South Zone:
Whangaruru beat Mangakahia - no result given
Tomarata 44 Otiria 14
Kaihu 26 Pipiwai 7
Moerewa/UK win by default
Southern win by default