Nottingham Forest scored four goals in the second half to complete an amazing comeback and keep up the pressure for automatic promotion from League One.
The relegated Bees took a shock lead when Thomas Pinault chipped home and Charlie Ide smashed in to make it 2-0.
However, David Prutton headed in and then set up Kris Commons to level, though he appeared to handle the ball.
Jack Lester then fell theatrically to earn a penalty which Grant Holt scored from, and Commons lobbed a fine fourth.
Brentford: Nelson, O'Connor, Frampton, Griffiths, Keith, Leary (Charles 90), Pinault, Mousinho (Willock 79), Brooker, Owusu, Ide (Montague 77).
Subs Not Used: Masters, Osborne.
Booked: Nelson, Leary.
Goals: Pinault 16, Ide 47.
Nottm Forest: Smith, Curtis, Chambers, Breckin, Wright (Morgan 84), McGugan (Gary Holt 81), Prutton, Perch, Commons, Grant Holt, Lester, Morgan (Bennett 90).
Subs Not Used: Pedersen, Power.
Booked: Grant Holt, Lester.
Goals: Prutton 52, Commons 68, Grant Holt 74 pen, Commons 90.
Ref: R Beeby (Northamptonshire).