Tom Denton headed in Jak McCourt’s corner to give Chesterfield the lead at half-time.
But Joe Sbarra equalised from close-range and then Kyle Hudlin headed the winner three minutes into four of added on time.
It was James Rowe’s first defeat as manager in seven games as Blues boss after a great start to his tenure.
Here are Liam Norcliffe’s player ratings from the match...
1. Kyle Letheren 5
Letheren has been in good form with five successive clean sheets but he will be disappointed he did not keep out Kyle Hudlin's late header which squirmed in. His kicking could have been better and James Rowe told him as much from the touchline. Letheren held his hands up after the game and acknowledged he should have stopped Hudlin's winner, Rowe said. Photo: Phil Tooley
2. Josef Yarney 5
Yarney came into the starting line-up at right wing-back with George Carline suspended. He was caught out of position a few times and assistant boss George Foster was barking orders for him to 'get back' and 'tuck in' quite often in the first half. He almost pinched a winner for Town at 1-1 after a scramble in the box. Photo: Phil Tooley
3. Will Evans 6
Not as good as what he has previously been under Rowe. Went long with his passing a bit too much instead of stepping out with the ball which is what we have seen in the last month or so. One weak back header to Letheren caused a heart in mouth moment. Photo: Phil Tooley
4. Haydn Hollis 6
A fairly steady performance from Hollis. Unfortunately the centre-back got dragged out wide for Solihull's winner as they countered. Had he been in the middle then he probably heads the cross clear and Hudlin does not score. But it was not really Hollis' fault because he was outnumbered. Photo: Phil Tooley