Defensive errors prove costly for The Bees as Wednesday take three points with a brace from Grant Holt and another from old-boy Lloyd Owusu.
It was rough justice for The Bees who controlled the first-half but were undone by poor defending in the last seven minutes. Such was Brentford dominance that Wednesday's first shot on target was a weak effort in the 21st minute from Grant Holt that was easily saved by Paul Smith.
In the 38th minute, Wednesday took the lead with a goal totally against the run of play. Stephen Hunt tried in vain to clear off the line as Grant Holt headed home Brian Barry-Murphy's right-wing cross.
The visitors doubled their lead in first-half injury-time, as dithering in the Bees' box led to a volley from Grant Holt beating Paul Smith from eighteen yards.
Wednesday survived a penalty claim by Tony Rougier in the 57th minute, and wrapped things up from a header by ex-Bees Lloyd Owusu, who was left in the box unmarked to head the third and final goal.