Until that fateful minute, Thistle had seemed to have the measure of a Marist side who had the advantage of familiarity with the artificial surface of Arena Turf.
But once Marist had the lead, they looked more assured.
It was only two outstanding saves from skipper Mitchell Stewart-Hill — a one-on-one stop in the 73rd and a close-range fingertip effort in the 84th — that kept the Jags in with a chance of sharing the points.
Thistle had come close to scoring earlier, notably through Somerton midway through the first half, when he appeared to have the goal at his mercy. But Marist goalkeeper Nick Hayward’s desperate, scrambling save cleared the danger.
The half ended on a sobering note when Thistle leftback Ander Batarrita had to be helped from the field after being injured in a tackle with Marist captain Adam Cowan.
Daniel Venema came on for Batarrita just before the break. Campbell Hall came on for Oska Smith in the 63rd minute, and Davie Ure came on for Ash McMillan in the 77th.
Thistle’s starting line-up was Stewart-Hill in goal; Sam Patterson and Batarrita as fullbacks, and Finn McAuley and Cai Maclean as centrebacks; holding midfielders Nick Land and McMillan behind attacking midfielder David Salmon; and Sam Royston, Somerton and Smith up front.
In the other Central Federation League game played on Saturday, Palmerston North United beat Taradale 2-0 at Memorial Park, Palmerston North.
This Saturday, Thistle continue their run of away games against Palmerston North United at Memorial Park.