Oldham snatched an unlikely draw after a controversial penalty in the fifth minute of injury-time.
Brentford's Andy Frampton is distraught after the penalty award
The Bees took the lead on the hour when Garry Richards glanced home a header and with five minutes left they went 2-0 up through Joe Keith's clever chip.
Leon Clarke immediately headed in Paul Warne's right-wing cross for Oldham.
And the play-off hopefuls grabbed a point when Sam Tillen was adjudged to have handled in the box and Clarke stepped up to power home the equaliser.
Brentford: Nelson, O'Connor, Frampton, Kuffour (Griffiths 89), Shipperley (Owusu 69), Richards, Tillen, Keith, Mousinho, Ide (Taylor 81), Leary.
Subs Not Used: Abbey, Pinault.
Goals: Richards 59, Keith 85.
Oldham: Pogliacomi, Rocastle (McDonald 62), Gregan, Haining, Wellens, Aljofree, Warne, Taylor, Liddell (Glombard 64), Eardley, Clarke.
Subs Not Used: Blayney, Roque, Edwards.
Goals: Clarke 86, 90 pen.
Ref: A Hall (W Midlands).