Bradley Wright-Phillips and Marcello Trotta were on target in a 2-0 win for the Bees at Griffin Park as Alex came back down to earth with a bump following Sunday's Johnstone's Paint Trophy final triumph over Southend.
"The players were disappointing after the terrific performance on Sunday," Davis said. "They were were too blasi and sloppy in the warm-up and that's how we started the game.
"They might have been tired but I don't want to make excuses for them, they have to do better than that. They weren't prepared physically or mentally and I have had a go at them for that.
"We didn't compete for the first 20 minutes but we never looked like scoring all night. We could be playing now and we still wouldn't have scored.
"When you only have three or four players near your level you aren't going to win any football match.
"Brentford were decent and are one of the best teams we played. They are competitive and powerful with a threat up front and they have a lot of experience which we are lacking."