Brentford were forced to play without talisman forward Ben Burgess who was suffering from a hamstring injury whilst Darren Powell was only fit enough for a place on the bench.
Brentford stated well and were the better team in the first half with Lloyd Owusu flicking a Paul Evans cross just past the post and Michael Dobson heading over from another Evans free kick. Dobson had another effort go over with a cross-cum-shot.
The first half was a mainly quiet affair with neither side able to get completely on top. Phil Clarkson had Bury's best effort but shot tamely into the arms of Paul Smith.
Brentford's chances in the game, and for the rest of the season, took a huge setback when Martin Rowlands had to limp out of the action just after the half hour to be replaced by Mark Williams.
The second half was a much better 45 minutes for the neutral with lots of action, although it was one Brentford fans will want to forget. Bury took the lead after 47 minutes with a splendid goal. Brentford failed to properly clear a corner and Billy volleyed home into the top corner from the edge of the area leaving Smith helpless. They should have extended their lead minutes later when Jon Newby was one-on-one with Smith but the young stopper saved with his legs.
Brentford pushed forward looking for an equaliser but never created anything clear-cut and were hit by a sucker punch after 74 minutes. Newby got clear on the left and squared for Billy. He rounded Smith and knocked the ball into an empty net to spark wild celebrations amongst the home fans and players.
Brentford brought on Eddie Hutchinson for Steven Sidwell and Hutchinson had Brentford's best chance of the game near the end but he headed harmlessly into the arms of Paddy Kenny. Owusu also had an effort cleared off the line as Brentford looked for a way back but it never came.
Brentford left with their heads bowed knowing they had lost ground to their promotion rivals in a winnable game and with three weeks of the season left it may turn out to be a disastrous defeat for their automatic promotion aspirations.
Brentford: Smith, Dobson, Anderson, Theobold, Ingimarsson, Rowlands (Williams), Evans, Sidwell (Hutchinson), Hunt, Owusu, O'Connor
Chris Wickham