A 90th-minute Chris Atkinson own goal meant Chesterfield lost to Fleetwood and fell to their second home defeat in a row.
The Cod Army had taken an early lead when Steven Gillespie capitalised on some poor Chesterfield defending.
But the hosts pegged their opponents back when Tendayi Darikwa's volley from the edge of the area was deflected in.
However, in the dying moments Atkinson mistimed a clearance from a Fleetwood free-kick to gift the visitors victory.
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Chesterfield caretaker manager Tommy Wright told BBC Radio Sheffield:
"I thought it was a decent performance against a good side.
"I thought second half was probably even-steven we missed a great chance and they've scored.
"It was a great chance for [Craig Westcarr], it was one each, but that's the thin line between winning and losing.
"They get a chance at the other end... it's disappointing, but I thought the performance was good."
Fleetwood Town manager Micky Mellon told BBC Radio Lancashire:
"In the first half, I thought we gave a really good account of ourselves.
"Apart from the goal, we had five really good chances to make the score more comfortable for us.
"But Tommy gets Chesterfield going with a lot of spirit and they got themselves back into the game.
"We stayed organised, kept being dogged and we knew that eventually we would try and play our way back into the game.
"To get a goal right at the very end - we're obviously delighted."