Brentford were made to pay for hitting the woodwork with two penalties as they were beaten by Play-Off rivals Stevenage.
Clayton Donaldson fired a first half spot kick against the bar and Sam Saunders hit the post with one in the second period.
Moments after Saunders' miss, Craig Reid opened the scoring for the home side and they made it safe when Luke Freeman smashed in a second just past the hour mark.
Saunders found the net with a curling free kick in the dying seconds but Brentford could not find the leveller and Stevenage took the points with a 2-1 win.
The Hertfordshire club climbed to sixth in League One with the victory and are five points ahead of The Bees with just two games remaining, all but ending Brentford's Play-Off hopes.
As was to be expected, with so much at stake, the teams spent much of the first quarter of the match playing at arms length.
It soon became apparent Brentford were the better footballing team but Stevenage have not got themselves in to the Play-Off race by allowing others to play.
They hassled and harried Brentford and only when The Bees put together lots of passes did they look dangerous.
Donaldson had an early header blocked and Chris Day held on to a curling Saunders shot.
Toumani Diagouraga also had a shot blocked but Stevenage could have been ahead when Michael Bostwick fired inches wide and Freeman did likewise after a run form deep.
The crucial moment of the first half came just past the half hour.
Donaldson won a header and Clinton Morrison forced a mistake out of Jamaal Lascelles, getting goal side of the defender and forcing the Stevenage man to bring him down.
Referee Carl Berry awarded to penalty but chose to only book Lascelles when he could have shown a red card.
Donaldson waited for Day to dive and hit the penalty down the middle but went just too high and the ball cannoned away off the crossbar.
Brentford were on top at that stage - having switched Donaldson to a central role from his starting position on the left - and went close again soon after when Jonathan Douglas blasted wide after a move involving six or seven players and more than 20 passes.
But Stevenage could have gone in ahead - Freeman pulled a shot wide from 15 yards, with Mark Roberts unable to turn the shot towards goal, and Patrick Agyemang shot wide when well placed.
Brentford started the second half brightly and when Donaldson and Morrison combined, the former raced in to the box - Jon Ashton brought him down and Mr Berry awarded another penalty.
This time Saunders stepped up and he sent Day the wrong way, however the ball bounced off the inside of the post and re-bounded back in to the arms of the Stevenage goalkeeper lying by the other upright.
Three minutes later Brentford were punished for their profligacy when Lawrie Wilson darted down the right and put in a cross, Reid controlled it, turned and fired in a low shot to put the hosts ahead.
They almost doubled their lead when Freeman darted down the left and picked out Lascelles with a cross, the right back fired in a shot that Karleigh Osborne did well to block.
But Stevenage did not have to wait long for their second - Adam Thompson lost the ball to Freeman and the wide man cut inside and fired an unstoppable shot from 25 yards that found the back of the net via the near post.
Brentford tried to find a way back - Osborne headed just wide and Saunders, who provided the corner for that chance, went even closer soon after.
Douglas spread the play and Harry Forrester got in behind the defence, he picked out Saunders with a cut back and the attacking midfield player looked set to reduce the arrears with a low shot back past Day but the goalkeeper somehow saved it with his feet.
Osborne blocked an Agyemang shot and Simon Moore tipped a Freeman shot over but most of the action was at the other end.
Donaldson's header from a Jake Bidwell cross was saved and the striker shot well over.
Stevenage tried to attack on the break and Moore saved at the feet of Chris Beardsley and John Mousinho before the former fired in to the side netting.
A Donaldson shot on the swivel was deflected wide before Brentford pulled one back in the last minute of normal time.
Forrester was felled on the edge of the penalty area and Saunders curled a free kick past Day and in to the top corner.
The Bees were throwing everything forward, bringing Leon Legge on as an emergency centre forward, but could not find an opening and Stevenage took the points.
Stevenage: Day; Lascelles, Ashton, Roberts, Laird; Long (sub Byrom h/t), Wilson, Bostwick, Freeman; Agyemang (sub Beardsley 77 mins), Reid (sub Mousinho 65 mins)
Subs (not used): Myrie-Williams, Slew
Bookings: Bostwick (14 mins), Lascelles (31 mins)
Brentford: Moore; Thompson (sub Forrester 64 mins), Osborne (sub Legge 77 mins), Dean, Bidwell; Logan, Douglas, Diagouraga, Donaldson; Saunders; Morrison
Subs (not used): Balkestein, Bean, McGinn
Bookings: Douglas (72 mins) (tenth of season), Saunders (82 mins) (sixth of season), Bidwell (90 mins) (fourth of season)
Attendance: 4,256 (1,231 Bees fans)
By Chris Wickham