Thistle eventually won 8-1 – with Jimmy Somerton scoring four goals – but only got away late in the second half after leading 2-1 at halftime.
The win lifted Thistle into fourth place on 22 points.
They are one behind Heavy Equipment Services Gisborne United, who drew 2-2 with Maycenvale in Hastings.
Napier City Rovers Reserves, who thrashed Napier Marist 9-0, lead on 27 points on goal difference from Havelock North Wanderers, who beat Port Hill United 2-1.
Thistle and Gisborne Boys’ High School (GBHS) were without regulars through injury or suspension.
The Sebastian Itman-coached students had only nine first-team squad members available, so brought in three from their Second XI, who had finished their Tairāwhiti league game only 30 minutes prior.
It took Thistle just two minutes to show their intentions – captain Cory Thomson putting a ball through to goal-scoring machine Jimmy Somerton, who smashed his shot into the top left corner, giving GBHS goalkeeper Aiden Armstrong no chance.
Six minutes later, Thistle winger Alex Shanks made one of his many good runs down the left flank and provided a peach of a pass to Thomson in the six-yard box and he guided the ball home.
It was threatening to be a cricket score, but after Somerton was unable to take advantage of some good chances, the students stunned Thistle with a screamer of a goal ... Jacob Adams made a superb run through the middle of the park and linked with Kyran Lasenby, who put in a fantastic cross for Korbin Wigglesworth to belt home with a ferocity that nearly broke the back of the net.
River Somerton had to leave the field in 39th minute, meaning GBHS were down to no subs for the remainder of the match.
Leading only 2-1 at halftime, Thistle faced stern words from coach Cramer.
They responded as they had started the first half, the ball going straight down the GBHS defensive end and Somerton becoming provider for Thistle’s player of the day David Salmon to unleash a low shot into the bottom right corner of the net.
GBHS were reduced to 10 men in the 75th minute when Casimir Schaub – who had replaced River Somerton – left the field.
The students battled on, their back three defending as if their lives depended on it. But having given everything, the dam finally burst with seven minutes to go.
Somerton made it 4-1 in the 83rd, completed his hat-trick from the penalty spot five minutes after and scored his fourth a minute later.
David Ure and Daniel Venema scored well-taken goals to complete the late surge.
On paper it was a comfortable win, but coach Cramer was far from happy.
“We were average today and we need to improve a lot more next week,” he said.
GBHS assistant coach Darren Larkins was proud of their efforts.
“We were completely in the game in the first half and unlucky not to go into halftime even.”
He paid tribute to the Second XI players who backed up and gave player of the day to Wigglesworth, who worked tirelessly and took his goal opportunity well.
Gisborne United headed south to take on Maycenvale United with only a point separating the sides.
Dakota Lucas scored in the sixth minute to put the home side in front.
It took the Dane Thompson-led United another 25 minutes to finally find the back of the net – centre back Jonathan Purcell heading home a Malcolm Marfell free kick.
Coach and striker Josh Adams put his side ahead in the 38th minute when he finished off a Campbell Hall cross from the left.
However, 18 minutes into the second half, Hall was given his marching orders after being yellow-carded twice from the same incident.
Maycenvale captain and striker Liam Shackleton scored 15 minutes later.
United were down to nine men for 10 minutes late in the game after Aaron Graham was given a dissent yellow card.
But even with a two-man disadvantage, coach Adams said they had four or five good chances to grab a winner.
United are at their home Harry Barker Reserve against Taradale at 12.30pm on Saturday, Thistle host Napier Marist at Childers Road Reserve at 2.45pm, and HSOB-GBHS are away to Port Hill.
