A penalty by James Ferry and a late goal by Tom Field gave The Bees' Under-15 side victory in their first fixture in the prestigious tournament.
The Bees took an early lead after eight minutes when Daniel Webster was crudely taken down inside the box.
Ferry calmly stepped up to fire his penalty low into the bottom corner of the net.
The home side were roared on by the hundreds of locals and looked to strike back immediately.
They had a couple of half chances but lacked that bit of quality to find the back of the net.
A County Londonderry corner was flicked on at the near post but headed wide of the target and an effort across the goal set up another chance that was fired over the bar.
Brentford could have doubled the lead just before half time when Seika Jatta raced clear of the defence and rounded the keeper, but he was nudged off the ball by the last defender as he was about to roll it into the empty net.
Jatta was in the thick of the action immediately after half time when he again found the goalkeeper in no mans land - as the striker was at a tight angle he found Herson Rodiguez Alves on the edge of the box but the midfield player dallied too long and the chance was lost.
Courtney Senior looked threatening throughout and he created another chance for Jatta that was deflected wide for a corner.
The home side were very physical and were pumping lots of balls into the box.
On most occasions goalkeeper Jake Lewis dominated his box and collected the balls.
On the one occasion that he failed to clear the ball the referee deemed he was fouled.
This was much to the annoyance of the home side as the ball was rolled into the empty net.
Despite the Londonderry pressure The Bees sealed victory late into the game.
Senior expertly controlled a beautiful through ball on his chest before racing into the box, his shot was charged down but Field was on hand to fire the ball into the bottom corner of the net.
Londonderry had an effort just wide in the final seconds but The Bees secured maximum points.
Head coach Danny Buck was delighted with the victory.
"The boys showed good character and desire to play to the Brentford philosophy even despite intense pressure from a well organised County Londonderry side," he said.
"The team showed glimpses of the football that they are capable of particularly with the two goals but we must improve and show more consistency if we want to continue to progress in the tournament.
"We are pleased to get three points on the board and now must work hard off the pitch tomorrow on our recovery day to get ready for the CSKA Moscow game on Monday."
Brentford: Jake Lewis; Daniel Webster (sub Romayn Pennant 40 mins) , Andrew Mills, Audrius Laucys, Ben Peden; Tom Field, James Ferry (C), Herson Rodiguez Alves, Jordan Watson (sub Reece Cole 50 mins); Courtney Senior (sub Bradley Clayton, 58 mins), Seika Jatta (sub Rimelle Straken 58 mins)
Subs (not used): Jordan Carey, Courtney Austin, Mikael Bongili