Pompey had played on the front foot and with a high tempo during an entertaining first half against Bolton.
But it finished goalless and they then fell behind to a close-range Dion Charles finish shortly after the interval.
Facing a side who had won seven of their past eight League One games, it would have been easy to collapse.
So John Mousinho credits the response of the Fratton faithful, who immediately turned up the volume to urge their team on.
And it worked, with Ryley Towler bagging a brace to flip things around before Colby Bishop wrapped up a remarkable 3-1 victory.
The Blues boss said: “It was a brilliant performance after going behind against a really good side who have turned other teams over – home and away.
“We reacted to that and not only did we get the equaliser, we went on to score the second and then the third.
“I heard the noise coming from the Fratton End after Bolton scored and you could see that just lifted the lads.
"They could see that we’d been slightly unlucky in the first half and decided to back the boys, who responded to that."
“Sometimes that can drain the life out of the crowd, but it was the complete opposite on this occasion.
“They could see that we’d been slightly unlucky in the first half and decided to back the boys, who responded to that.
“We didn’t make any changes from Saturday and all the boys showed their physicality and intensity, while we’ve got guys coming off the bench and doing the same.
“I’m absolutely delighted for Ryley and that’s what it’s all about for these players. If you can’t enjoy that, then you won’t enjoy any football match.”
Pompey do not have the luxury of basking in their latest victory, with the games now coming thick and fast.
Mousinho said: “This result is only as good as what we back it up with on Saturday, but we can certainly take confidence from it.
“I sound like a broken record, but the boys have to be professional and recover properly, doing the right things on their day off.
“The schedule is relentless and I don’t want to take anything way from a brilliant win, but we must be ready to go again at Cambridge.”