Bees take the points on wet Boxing Day.
The U’s made a number of changes to their starting eleven but found themselves one down within three minutes of kick-off.
The points may have escaped the U's grasp, but boss Joe Dunne will take some solace in how his side approached the game after that nightmare start.
However, it was the visitors who got what would be the crucial fourth goal in the game, as they tucked home from close range late on in the match.
Drey Wright's first professional goal gave the U's hope and, led by a superb performance from captain Kem Izzet, they pushed the visitors back as the game wore on.
The home side were left with a mountain to climb as they went down to ten men and found themselves two goals down within the first ten minutes, but they stuck with it and gave the Bees a real game.
A brave effort was not enough to save the U's from a Boxing Day defeat, as they fell to a 3-1 defeat to Brentford.
A ball was swung over from the left and nodded back to the waiting Trotta, who was given time to turn and spin and fire a shot high into the roof of the net past Cousins.
The home side responded well, with Wright and Gilbey combining for a cross that Massey couldn’t quite reach, as they looked for an instant equaliser.
The U’s bad start got worse nine minutes in though, when loanee Thompson saw red for a foul on Donaldson. A ball through the middle had opened the home side up, and the defender caught the striker as he reached the edge of the box.
That decision was immediately punished, as Forshaw stepped up to curl the resultant free kick into the top corner beyond the despairing dive of Cousins.
Okuonghae was the man introduced to shore things up at the back as he replaced Gilbey on eleven minutes, and the big defender was in the right place to block Donaldson’s shot from the edge of the area.
Just before that chance, Eastman had sidefooted one wide from a free kick into the box and, on eighteen minutes, he went close again as he slid a set piece from distance wide of the upright.
But the U’s were given hope midway through the first half as a superb tackle from Izzet sent Drey Wright away down the left hand side.
The winger took on Hodson and cut inside, dropping his shoulder past Dean and smacking a shot into the bottom corner to halve the deficit.
White then cut inside from the other side and hit in a powerful left footed shot that tested Lee in the visitors goal, as the U’s sought an equaliser.
From the resultant corner, though, the Bees hit the home side on the counter and Forrester looked like he might extend their advantage. However, he scuffed his shot and Cousins saved well.
Wright was enjoying himself down the U’s left, up against full back Hodson, but the U’s were having to be patient as they attempted to keep their shape and stay in the game at 2-1 down.
The U’s were right back in the game just before half time as they chased down a loose ball and as they won it, Adeyemi caught Izzet. He’d already been booked for catching the U’s skipper and this time saw red.
From having looked like they might be out of the game early on, they got to half time with everything to play for.
Chances were limited after the interval, but the U’s were working exceptionally hard to force their way back into the game.
Led by the inspirational work of Izzet and the youthful verve of Wright, they were testing the Bees defence and boss Joe Dunne also introduced Freddie Ladapo for his U’s debut midway through the half.
The young forward made two or three darting runs not long after his introduction and the U’s fans, having seen Wright’s impact also saw that the front man could do the same.
One such run forced a fine low stop out of Lee and, from the resulting corner, Izzet turned one just over the bar.
However, the U’s were put back on their heels by a third Brentford goal. It was knocked down by Donaldson and although Cousins saved the initial effort, Dean was on hand to slide home.
The U's left the pitch to warm applause from their supporters who had seen them battle hard, but ultimately end up pointless by the time referee Gavin Ward blew his final whistle.
At the other end, Bean forced a great save out of Lee with a fierce volley on the angle, but the match was beyond Dunne’s men as the game entered injury time.