Armand Gnanduillet headed home deep into injury time to condemn Blues to their first League 2 defeat of the season as Chesterfield won 2-1 at the Proact Stadium.
Gary Roberts’ terrific free-kick put the hosts ahead on the hour mark before Freddy Eastwood got his third in three games to draw Blues level.
Blues thought they had done enough to earn a point, but substitute Gnanduillet had other ideas and headed home deep into injury time as Blues suffered their first league defeat of the season.
Phil Brown made just one enforced change to the side that beat Northampton Town last weekend as Conor Clifford replaced the injured Marc Laird. With Mark Phillips still out through injury there was a place on the bench for young defender Josh Banton.
The hosts, widely tipped for a serious assault on promotion this season, started brightly and created the first real chance of the game. Marc Richards latched onto a ball over the top and beat Daniel Bentley to it, but the striker couldn’t find the target with the goal empty.
John White then created Blues’ first chance of the game, but Tommy Lee in the Chesterfield goal saved his left-footed strike comfortably.
Both sides were playing some excellent football in an end-to-end encounter but it was the hosts who almost broke the deadlock. Jay O’Shea’s curling effort seemed destined for the top corner, but Bentley pulled off a tremendous save to tip it over the bar.
Blues themselves were also causing problems. Barry Corr released Freddy Eastwood who was denied by an excellent block just as he went to pull the trigger, before Clifford’s strike was deflected behind for a corner after excellent work from Anthony Straker.
The second-half began in the same way the first had ended but just before the hour, Chesterfield broke the deadlock. After Roberts had been fouled by Clifford, he stepped up and fired home an excellent free-kick from 30-yards.
But the hosts weren’t ahead for long as Blues drew level in the 68th minute. Corr and substitute Kevan Hurst were both involved in teeing up Eastwood, who smashed home from 18-yards.
Roberts was looking dangerous for the hosts and almost got his second of the afternoon from another free-kick. This time though Bentley was equal to it and beat the ball away to safety.
Blues thought they had done enough to earn a valuable point on the road but Chesterfield substitute Armand Gnanduillet had other ideas and headed home Roberts’ corner deep into injury time.
BLUES: Bentley; White, Prosser, Thompson, Coker; Atkinson, Leonard, Clifford (Hurst 59), Straker; Eastwood (Timlin 82), Corr (Cowan 77).
SUBS NOT USED: Payne, Reid, Banton, P. Smith.
BOOKED: John White; Conor Clifford, Luke Prosser