An excellent and relentless performance in a narrow losing cause against Thomas Tuchel's Chelsea in a televised FA Cup tie at Oakwell on February 11 has widely been cited as a 'game-changer' in the Reds' season.
After that unfortunate 1-0 loss against a Blues side who have seen their colours lowered just twice in 22 matches in all competitions under Tuchel, Barnsley embarked on a magnificent seven-match winning run.
But Ismael has revealed how a comprehensive 3-0 defeat early in his tenure at Cardiff on November 3 - on an evening when he was provided an crash course in what is required to succeed at Championship level in just his third match at the helm - similarly provided a valuable lesson and turning point.
It provided him with the clarity of thought in terms of what was required to turn around the club's fortunes. After that defeat in Wales, the Reds dropped to 17th place in the second tier.
Ismael, now preparing for the start of a play-off campaign with the Reds, who welcome Swansea City in the first leg of their semi-final on Monday night, said: "I think the first key moment was the game after Cardiff. We lost 3-0 and it was clear I had arrived in the Championship and knew exactly what we needed.
"The second was the game against Chelsea; the ‘game-changer’. I know it is two defeats.
“After it was the game against Brentford - three days after Chelsea. Why? Because we were incredible that day.
The mentality of the team against Chelsea was the game-changer and against Brentford, there was confirmation that now we can compete at that level and we are ready to continue.
"We have stayed all the time in that way. In the first time when we came into the play-off spots, we stayed there all the time and never dropped out and it showed how far the guys have improved their mentality and their performances to stay at that level."