The Spireites’ 15-game unbeaten run came to an abrupt half after falling to a 2-1 defeat to Southend United at Roots Hall.
Will Grigg scored his tenth goal of the season to put the Blues a goal up before two Southend goals in three second-half minutes.
Paul Cook made two changes to the side that beat Barnet last Saturday as Darren Oldaker and Michael Jacobs came in for Mike Jones and Armando Dobra.
After a fairly quiet quarter of an hour, Harry Tyrer was called into action as he did well to palm away Jack Bridge’s bouncing volley.
The Chesterfield goalkeeper was once again alert soon after to parry Harry Cardwell’s fierce half-volley.
However, as the game neared the half-hour mark, the Spireites got the opener when Jacobs’ wicked curling cross found Grigg, who poked home from a couple of yards.
Ryan Colclough tested David Martin on a couple of occasions, which the Southend goalkeeper was equal to.
After an even first half, Colclough looked to make the score line more comfortable with a shot that hit the side-netting.
On the hour-mark, Southend were awarded a penalty when Branden Horton fouled Harry Taylor in the area. Bridge assumed responsibility and placed the ball down the middle of the goal.
Three minutes later, Wes Fonguck’s pull-back ricocheted off Oldaker and squirmed past Tyrer.
The Spireites struggled after going behind and saw Dobra shoot wide and Tom Naylor have an effort saved by Martin.
In added time, Grigg latched onto James Berry’s brilliant cross but couldn’t keep his close-range prod down.
Despite the defeat, Chesterfield remain top of the National League and also stay five points ahead of Barnet.
Chesterfield: Tyrer, Mandeville, Palmer, Grimes ©, Horton, Naylor, Oldaker (Jones 65), Jacobs, Banks (Dobra 65), Colclough (Berry 87), Grigg.
Unused Substitutes: Freckleton, Quigley.