Delighted Cambridge boss Colin Calderwood hailed his side's defensive effort for causing one of the Carabao Cup's big first-round upsets.
Harvey Knibbs' sudden-death penalty won it for the Us after Brentford's Marcus Forss cancelled out Marc Richards' third-minute opener.
And Calderwood said: "We showed a lot of gumption to hang in there, and the longer the game went on the more we grew into it.
"I don't think Brentford really created anything clear-cut after they equalised and that shows how hard the boys worked for each other to restrict them, even when we were camped in our own half.
"It's a very good night and it will get us a few headlines and make people at the club feel good about themselves, which is always a good thing at this stage of the season."
He admitted post-training penalty sessions may have played a part in the upset, adding: "Some of the lads stay behind to practice and it paid off tonight, but they have ruined the penalty spot at the training ground and we can't afford that type of behaviour."
The League Two side's reward for beating one Championship outfit is an away trip to another, Swansea.
Brentford head coach Thomas Frank made nine changes to the side that beat Middlesbrough away and admitted his side needed to "find solutions" to break down defences.
"It was a classic cup game between a minor side and a team in a higher division. We dominated but they got the early goal and banked up defensively," said the Dane.
"We showed a lot of willingness in the first half but it didn't really click. The second half was much better in terms of passing the ball and moving it quicker but I expect us, even when we're playing against a back five, to create more because a lot of teams have one game plan when they come here.
"We need to find some better solutions to create even more chances but it's not always easy for even the best sides in the world. We can and will look at how we create more chances.
"We wanted to win and go through but it's always that balance between keeping players fit and getting minutes into them. We had players more than capable of winning the game but it just didn't happen."
