Ten minutes in second half cost U's dear.
The U’s made just the one change for the game at Griffin Park, with Morrison coming into the side for Gavin Massey.
And, as they pressed for the second, the Bees got level, before opening up a two goal cushion to earn a three point haul that was much needed for Uwe Rosler's side.
Magnus Okuonghae's powerful header looked like it was setting the U's on their way to a positive second half and they looked like they might get that elusive second that had been hard to find in recent weeks.
Three goals in ten minutes in the second half cost the U's dear on Saturday as they went from being in front to losing 3-1 at Griffin Park.
The game was fairly even stevens in the early stages, with Brentford having an odd half chance. Garbutt was the busier of the full backs as he looked to keep his man at bay.
There were shouts of handball when a Dean shot from a corner struck Taylor at close range, but the referee had no interest in the fans’ shouts.
The home side really should have taken the lead after fifteen minutes. A cross into the area found Saville, whose shot was saved superbly low to his right by Walker.
It squirmed free of his grasp to the awaiting Trotta, who had the goal at his mercy six yards out. With the home fans off their feet and celebrating, he somehow contrived to slice wide.
Chances were relatively limited for the U’s in the first half an hour, but Eastmond intercepted the ball just inside the U’s half and set Sears away.
He got the edge of the box and cut inside, curling an effort just wide of the far post for the U’s best chance so far.
Taylor was next to go close for the U’s, his header from Garbutt’s free kick sailing over the bar as he rose under pressure at the far post.
The Bees looked short of confidence, and on several occasions made simple mistakes in possession that stopped them turning the screw on the U’s.
The game was goalless at the break, but the U’s were in front within three minutes of the restart in the second half.
They won a set piece down in front of their own fans and Garbutt’s delivery came up trumps. He swung one into the centre of the area and Okuonghae stooped to conquer and powered home an unchallenged header.
The Bees tried to level with a Forshaw free kick, but he tried to feed it into the bottom corner and Walker turned it behind.
The home side had responded well to going behind, but the U’s were always well set up to attack on the counter.
The U’s were seeking a second and a class touch from Sears moved the ball into a position for him to shoot, and his second touch was a stabbed effort that forced a good stop out of Button.
Trotta was the next to go close, his low shot looked destined for the bottom corner as it clipped Taylor’s heels, but Walker did well to turn it away.
Massey replaced Morrison on 62 minutes, with the midfielder playing in behind a front two of Sears and Ibehre.
The U’s almost doubled their advantage not long afterwards as another fantastic delivery from Garbutt just missed the outstretched boot of Gilbey.
Massey had added an additional verve to the U’s display after his introduction, but saw the home side nearly draw level on 73 minutes.
Saville found space in the middle but clipped his header off the top of the bar. However, they were level sixty seconds later. A cross came in low from the right and Trotta finished low into the near post to make it 1-1.
And they were 2-1 up five minutes later. Eastmond lost the ball and Saville stepped forward to curl one in off the inside of the far post and back into the net.
And the match was to finish with that advantage for the visitors, as the U's continue to search for that important three points.
For the U's, it was to get worse, a further five minutes on. Another cross from the U's left found debutant Harris powering into the box and he powered home his header to make it 3-1.