Paul Cook was left rueing his side's disastrous start at Plainmoor after two goals in the opening nine minutes gave struggling Torquay a valuable three points in their quest for survival.
The Gulls, who had registered just one win in their previous 18 encounters, raced into a two-goal lead on the English Riviera courtesy of Notts County loanee Joss Labadie and top goalscorer Rene Howe.
Liam Cooper gave his side a glimmer of hope with just over 15 minutes remaining, but it proved to be too little too late for the Spireites who failed to close the gap on the League Two play-offs to just five points.
"Our game plan has gone out of the window," Cookie told Spireites Player at full-time.
"We knew Torquay would be fighting for their lives, we had them watched at Southend on Saturday they played really well.
"Unfortunately for us, we didn't start the game in any shape or form and we were second best for long periods and we ended up going 2-0 down.
"It's hard to come back from that. We gave ourselves a lifeline in the second half and to be fair to the players they did keep working and trying but the game had gone by then. We gave Torquay something to hang on to and fight for.
"We came here tonight to win the game because we knew we had to and it's hugely disappointing for everyone."
The Liverpudlian's side appeared to have turned a corner of late after registering three wins in their last four games having conceded just once in five games. It was also the first time Town had conceded a goal in the first half for a staggering 13 matches, a run stretching back to the 1-1 draw with Morecambe in December.
But Cook, who has seen his side register successive wins only twice this season, revealed the play-off dream may well be out of reach for another year following a campaign plagued by inconsistency.
"League tables don't tell lies," he said.
"Our inconsistency has been consistent this year. It is two steps forward and two steps back.
"Our season hinged on tonight. We brought great travelling support down and they go home very disappointed, as we all are.
"We know as a football club we must get better and that is the message to the players, it has been since day one.
"The expectancy for our club is to deliver and for whatever reason, we haven't."
Chesterfield welcome former manager John Sheridan back to Whittington Moor on Saturday, as he brings his struggling Plymouth Argyle to the Proact for the first time.
Sheridan guided the Spireites to both the League Two title and the Johnstone's Paint Trophy during his time as boss but was relieved of his duties back in August following two points from just three games and his new side are one of four teams fighting for their lives on 43 points.
With seven games left to play, Cook admitted his side would probably have clinch a maximum haul of 21 points to have any chance of a top seven finish but insisted his side bounce back.
"We're sick, we really are.
"By the time we've licked our wounds, it's seven wins will get you there but I think you have to be a little more realistic than that.
"We've got to make sure we keep going and lift everyone's spirits because when clubs are flat and ours will be, it's important we look forward to a brighter future."
You can watch Cookie's interview in full exclusively on Spireites Player.