The Matt Hastings-coached visitors did have their moments today but the youthful exuberance of Marist, a lower-tier Computer Care HB Premiership side, proved to be the difference.
Marist's Ben Lack made a surging run from almost 35m out from a counterattack in the 21st minute but goalkeeper Stewart-Hill saved Gisborne's bacon with a timely tackle after several defenders were left stranded from Lack's dazzling footwork.
Three minutes later it was another "ooh" moment when Marist striker Jake Murphy found himself in a one-on-one situation from point-blank range but Stewart-Hill got in the way again.
Marist's Ruben Thurston had a shot after a feeble cornerkick clearance from the Thistle defenders in the 29th minute but Stewart-Hill parried and the ensuing header from Mason Jones sailed over the crossbar.
Two minutes later, during a goalmouth melee, a Gisborne player seemed to have placed his arm on the ball but referee Harris, of Hawke's Bay, deemed it a ball-to-hand situation amid howls of protest from the parochial home fans.
It was Marist goalkeeper Ryan Todd's turn to be the saviour after thwarting a 30m drive from Thistle's David Salmon in the 41st minute but the follow up from Ander Batarrita skewed past everything in pitching wedge-like fashion.
Two minutes into the second half, Lack again had a golden chance to break the impasse in favour of the hosts but that spectre of Stewart-Hill just wouldn't go away, as he got up to parry the ball twice.
It wasn't until the 60th minute that Thurston drew first blood, 1-0, with a screamer from 30m out to catch Stewart-Hill off guard.
Temper frayed in the 66th minute with Thistle striker Joshua Harris and Marist's Jones throwing punches in the scuffle as calmer heads from both sides moved in to pull them apart.
Referee Harris wasn't having a bar of it, sending both the players off with straight reds for an early shower.
The carded pair exchanged pleasantries along the way to the tunnel to leave their teams a man down each.
Gisborne's best chance probably came in the 84th minute when, from a freekick, Joshua Adams came agonisingly close when he pushed the ball past his left upright from about 38m out.
However, Marist midfielder Josh Murphy came a fraction too late in the 87th minute to extending the lead but Stewart-Hill came to the rescue.
The writing was on the wall when teenager Josh Murphy latched on to a through ball in ref's time, beat a Gisborne defender before taking the ball on the right flank with the defender on his heels.
The Napier Boys' High School pupil beat the defender before squaring from inside the 18m box to Daniel Baxter to slot the ball into the net for a 2-0 victory.