The Londoners were lucky not to concede more as they crashed to their first away league defeat of the season.
There was no sign of a Carling Cup hangover after Chesterfield's midweek victory over Manchester City.
The home side totally dominated the first half and should have added several more to their three-goal tally.
The result was never in doubt after Caleb Folan ran from the halfway line to slide home the opener on the half hour.
Several chances had already gone begging before his effort and it was no surprise when Paul Shaw added a second seven minutes later.
Derek Niven's goalbound shot cannoned off keeper Stuart Nelson's chest into Shaw's path and he fired home from 15 yards.
Two minutes later Folan added his second side-footing home Paul Hall's cross after Kevin Hurst had torn the Bees apart down the left wing.
The visitors grabbed an undeserved lifeline on the stroke of half-time after Barry Roche beat Paul Brooker's shot away ans Adam Griffiths made the most of a goalmouth scramble to stab the ball home.
Early in the second half Chesterfield were forced to withdraw both Folan and Shaw through injury handing the initiative to the Londoners.
But despite having the ball for long periods the Bees never created a goal scoring chance.
It was Chesterfield who found the net again when substitute Colin Larkin made the most of a poor clearance only to be ruled offside.
Chesterfield's rhythm completely vanished as they struggled to clear their lines.
Substitute Wayne Allison's lack of pace upfront was embarrassing and a quicker striker may well have punished Brentford's eagerness to push forward.
In a last desperate effort defender Matt Heywood was pushed up front but never got a touch of the ball in the last ten minutes.