The home side began brighter and nearly went in front in the fourth minute when Michael Turner saw his header superbly clawed out by Marton Fulop.
Having weathered the early storm, Roy McFarland's men began to get a stranglehold on the game but they had to wait until the 25th minute to create their first real chance.
Mark De Bolla found himself bearing down on goal but his low angled shot was comfortably dealt with by Stuart Nelson in the home goal.
That chance gave Chesterfield new-found confidence and, with Brentford struggling to pick up their early tempo, the visitors went ahead against the run of play in the 38th minute with a superb goal on the counter attack.
Carlos Logan provided the assist with a through ball to Bollo who found himself in an identical position to earlier but this time he fired home under the body of Nelson.
Chesterfield then had a chance to double their lead just before the break but Logan mis-cued his effort.
The Bees started well again after the break but it was Chesterfield who scored again, this time a great cross from full-back Alex Bailey was met by Wayne Allison whose header gave Nelson no chance.
However, the two-goal lead was almost too good to be true for Chesterfield given the amount of pressure Brentford had exerted.
And within two minutes Deon Burton halved the deficit by turning in Kevin O'Connor's cross.
Brentford were now in the ascendancy and completed the comeback when Chesterfield failed to clear their lines and Jay Tabb's 20-yard shot was deflected past Fulop.