The boss was concerned especially with his side's first half performance - which saw Sone Aluko give the visitors the lead despite some good work from Daniel Bentley .
Tom Cairney's late strike wrapped up all three points for Fulham - and it was a well-deserved victory for the visitors in the eyes of the Brentford manager.
"First half we weren't good enough. We had too many of five and six out of tens which isn't good enough at this level," Smith said.
"They had more like sevens and eights out of tens and they got the result.
"It's a local derby, I expected them to start quick. We didn't help ourselves, we played in front of them and they allowed them to come and press us even more.
"They deserved to win."
However, Smith is hoping that his side can improve again after the international break and kick on from there.
He said: "I think tonight showed our average age - there's a little bit of inexperience. One of the youngest in the league.
"But after last week I felt that we'd be good enough to go and put in a performance. Too many players didn't perform at the level that was required tonight.
"We won last week and hopefully we can go and get a win after the international break.
"It's disappointing that we've lost a home game today, we've had chances in the second half but so have they. After last week it's a disappointment."