Johnson said: "It was very disappointing, you don't want to get beaten 3-0 at any level. But the run has come to an end because we didn't do our stuff on the pitch.
"We had two or three half chances early in the game and if we had been able to put those away, it might have been a different story.
"At 2-0 we threw everyone forward and they came and punished us on the break. We should have maybe made more of our earlier chances.
"Credit to Barnsley they got on top, got their runners into the box and most importantly they were clinical where it mattered."