Paul Cook said there can be no excuses for his side’s home defeat to Southend United on Saturday.
Gavin Tomlin’s breakaway goal seven minutes from time gave the visitor’s an unlikely three points and moved the Shrimpers back into the play-offs in League Two.
Chesterfield missed a flurry of good opportunities but couldn’t find a way past Paul Smith.
Marc Richards came closest for the hosts when his 30-yard free kick hit the woodwork.
And the Spireites manager said the result wasn’t a fair reflection of the game.
He said: “We are disappointed for the lads, they’ve put a fair level of performance in but without the result.
“That will happen over a 46 games in the season. Sometimes you’ll go away from home, like Southend have done today, and get the run of the green.
“There can be no excuses, we’ve had 90 minutes to win a football match. We just have an Achilles’ heel that when we get stretched and perform at a tempo we’re not comfortable with, we become a little bit loose.”
Winger Tendayi Darikwa picked up a dead leg during the game while Armand Gnanduillet came off the bench to make his debut.
“Armand was bright and lively, and showed the fans he’s got something we can work with,” added Cook.
For more on the Spireites, and in depth interviews with new signings Armand Gnanduillet and Richard Brindley, pick up this week’s Derbyshire Times - out Thursday!