Thomas Frank was left frustrated by defensive problems, but admitted his team lost "fair and square".
The Bees were beaten 3-1 by Newcastle at St James' Park and were duly knocked out of the Carabao Cup.
Brentford experienced some defensive disruption before the game after they made a late change to the starting line-up, with Nathan Collins replacing Sepp van den Berg.
They were then handed another blow 14 minutes into the game when Ethan Pinnock was unable to continue, and Frank believes his team conceded "three soft goals".
He said: "We on the day met a better team than us, we lost fair and square over the 90 minutes.
"I think the main bit I'm disappointed with is the defensive side of the game, we gave - in my opinion - three soft goals away that we can't give away.
"We need to avoid all three and they are definitely avoidable, so that's the disappointing thing that we couldn't do that because it gave us a mountain to climb."
