Reynolds made 27 and McMurray 28, while Mark Kennedy took 2-14 off four overs for Ngatapa.
The Green Caps responded with 122 all-out in the 22nd over, largely thanks to 56 by opener Hoffman Haasbroek, who smashed three consecutive fours to end spinner Reynolds’ opening over before the latter came back to snare four wickets on the trot in his second over.
Kennedy contributed 18 with the bat while Reynolds finished with a five-for and Callum McInnes nabbed two wickets.
Jeff Chambers’ 41 and Ollie Needham’s 23 retired anchored the Presidents’ 123-5 as they comfortably chased down Horouta’s 120 all-out in the 19th over.
George Judd picked up 2-19 off three overs for Horouta.
Matthew Kotuhi (24) was the only run-scorer of note for Horouta as the HSOB bowling attack put the squeeze on.
Bradley Clark conceded just seven runs in his four overs, which yielded him one wicket.
Gisborne Boys’ High T20 Challenge Cup scoreboard
The Blues & Royals 131-5 (Jasper Sutherland 39, Jasper Shand 37 not out; Finnbar Whitfield 1-10-4, Pranash Senthooran 1-24-4, Bihandu Withanage 1-34-4) def The Life Guards 32 all-out in 6.2 overs (Finnbar Whitfield 15; Rian Lewis 1-1-1, Kushan Malimage 1-4-1.2, Jack Williams 1-10-2) by 99 runs.
The King’s Own 181-2 (Harvey Reynolds 101 retired, Jake Kirkpatrick 22, Charlie Hope 17no, Jed Reynolds 11; Tristan Walker-Daniels 1-22-2, Tristan Flamwell 1-44-4) def The Admiralty 108 all-out in 19.5 overs (Tristan Flamwell 32, Mitchell Van Zyl 32; Jake Kirkpatrick 2-11-3, Brandon Chari 2-12-3) by 73 runs.