Wayne Allison celebrated his 750th League appearance by scoring to give new club Chesterfield victory.
Allison pounced to convert Ian Evatt's to give Chesterfield a first-half lead.
Allison soon limped off injured but replacement Caleb Folan made it 2-0 when he headed home Mark Allott's cross midway through the second half.
Alex Rhodes' low drive found the net to give Brentford hope, but substitute Tcham N'Toya then cut inside and fired home from the edge of the area.
Chesterfield: Muggleton, Bailey, Blatherwick, Evatt, Nicholson,
Allott, Hudson, Niven, Innes (Davies 86), Allison (Folan 28),
De Bolla (N'Toya 73).
Subs Not Used: O'Hare, Richmond.
Goals: Allison 17, Folan 64, N'Toya 90.
Brentford: Nelson, Dobson (O'Connor 80), Turner, Fitzgerald,
Myers (Frampton 51), Tabb, Hargreaves, Talbot (Rhodes 61),
Salako, Rankin, Burton.
Subs Not Used: Lennie, Smith.
Goals: Rhodes 70.
Referee: E Ilderton (Tyne & Wear).