A moment of quality won the match for promotion chasing Fleetwood as experienced 53rd minute substitute Jon Parkin's defence-splitting first-time pass enabled fellow striker Jamille Matt to apply an equally good first touch finish.
After a dour, shot-shy first half Matt forced home keeper Martin Rice to save well at the start of the second half.
Recalled Rice also got a touch to deflect Antoni Sarcevic's angled drive from the right off the face of the far post as Town pressed for a crucial opening goal.
Hargreaves said: "We will be back in on Monday, dust ourselves off and get ready again. There's no other way in football is there? It's a cruel game, we know that.
"Obviously I am disappointed but I just said to the players as long as there is a breath left in me I will keep fighting and they will do the same. They fought like lions and I am with them, they know that.
"There's no problem with motivation sometimes out there it is about one spark of quality or a moment's lack of concentration that either gains or loses a goal. That's what it was today.
"It's all about concentration for 90 minutes and for one split second, some cover wasn't applied and you get punished.
"The longer the game is nil-nil and you don't score, one team is always going to nick it. We had enough chances and we didn't score but you have got to shut-up shop and we didn't. It's another cruel lesson to some footballers in there.
"We know we deserved more today but the game is gone and all I can do now is look ahead to Tuesday."