Harrison Gregory struck first in the 20th minute when he breached the Thistle bunker from almost 40m out, keeping the defenders guessing on which attacking teammate he was going to pass to from the rib of the field.
Gregory instead called their bluff and wove his way through to drill the ball past Gisborne goalkeeper PJ Goodlett for a 1-0 lead.
Four minutes later Thistle midfielder Nicky Land almost equalised, with 15-year-old goalkeeper William Kimber beaten but the crossbar denying him the goal.
The hosts stuck to their processes and reaped the rewards in the 32nd minute when Bjorn Christensen found the net for 2-0, after Gregory dropped a speculator into the box and captain Jared Bloor outmuscled keeper Goodlett before crossing the ball to the far post for an elementary finish.
Changing to 4-3-3 formation in the second spell, Gisborne opened up the game and pulled it back to 2-1 in the 53rd minute through leftback Jake Roberts, who tested Havelock North High schoolboy Kimber from about 45m out on an oblique angle.
Stung into action, the villagers responded through Bloor in the 61st minute to make it 3-1 after he again won the arm wrestle against the keeper to stab the ball in amid suggestions of offside, which referee Gareth Sheehan didn't buy.
That prompted Roberts to replace Goddett with regular keeper Mark Baple but eight minutes later Havelock made it 4-1 following a goalmouth melee when teenager William Callaghan poked a ball in at the far post from a Bloor cross.
However, the fans had some anxious moments when Land narrowed it to 4-2 on fulltime, chipping the ball over an advancing Kimber.
Two minutes into added time Cory Adams pulled the scoreline back to 4-3 with what can best be described as a feeble goal when Kimber fumbled a freekick from about 35m out.
Barclay was impressed wiith his young debutants - Lindisfarne College pair Josh Bayly and Callaghan, and Kimber.
"Lots of teenagers and their willingness to play, getting stuck in so the football bodes well for the [province] with a batch of players, not just for Havelock, but coming through across the Bay," he said, finding it a pleasure to be a part of that development.
Who the villagers play in the second round didn't matter to the team because they are keen to face unknown quantities and get outside their comfort zone.
"Last year we played Wairarapa United and it was amazing to go play at their ground against the likes of Paul Ifill and co, although the result will be whatever it'll be but it'll be a new experience for all of us."
Barclay's only reservation on Saturday was his troops' propensity to let in sloppy goals.
"We've been lucky it hasn't hurt us result wise so far but it will one day so we'll have to tidy up."
Coach Robertson felt his defenders had drifted to five in the back but it was a proven ploy at Childers Road Reserve.
"They probably changed their mind [after halftime] because they have enough senior players out there to do it," he said.
Thistle return to Guthrie Park for a league rematch on June 18 and possibly again in a top-four, bottom-four playoffs.
