The Bay got a run off the first delivery of the match, a wide from Kaden Cossill (2-11).
Opener Jett Whitaker was out for nought, caught by Farrell off the last ball of the first over.
Cooper Goodhew (3-5) bowled Akira Makiri (1), fifth man in, and gloveman Charlie Whitfield (0) — batting at No.7 — with the second and third balls of the 11th over.
Poverty Bay were 6-23 but Robbie Newlands (7), in at eight, kept out the hat-trick ball.
Ruan Ludwig, from No.10, made 11 not out and was the only batsman to reach double figures as the Bay was dismissed for 52 in 22 overs.
Cossill shared the new ball with left-armer Johnathan Gray (1-5), of Gisborne, and Blake Farmiloe, second change, took 2-6.
All three bowled out, the opening pair bowling two maiden overs and Farmiloe one.
The Māori pace attack is more than useful but they made as rocky a start with the bat as can be imagined.
Like Cossill, Poverty Bay left-armer Caleb Taewa (1-16 off three overs) bowled a wide to start his spell and then trapped Angelo Giacon leg before wicket with the first legal ball of the second over.
At first-change, Jonah Reynolds took 1-9 off two overs and captain McGuinness (1-16, three overs), relieved Taewa.
Pire Poi Wilson made 14 from No.3 before McGuinness got him lbw, that 14 being the highest individual score in the match: No.5 Brydon Rhodes took two off the second ball of the 10th over, bowled by medium-pacer Malsha Mahabalage, for the win by seven wickets.