Josh Scowen's penalty was overturned by the home side with two goals before the break.
"We got sucked in to them trying to bully us," said Johnson. "I was disappointed because we are a young group but you can't get bullied.
"We have to be physically and mentally stronger. Credit to them because they imposed their strength on us.
"After we scored we looked all right and comfortable. But we didn't see off the half.
"We need everybody now to help us. There are three losses on the spin in the league. We've got to make sure we go into our two home games positives and make sure everybody gets behind the group.
"It's decision-making and quality. Generally, our quality in wide areas left a lot to be desired.
"We had to be careful there would be no sendings off but he managed the second half quite well. There were too many people trying to run with the ball. We were getting overpowered by their running power.
"I fancied Michael Smith to score the chance he had. But, we lost possession too many times up front. That gave their full-backs quite a lot of room and we were caught out."
Lee Johnson also confirmed Marley Watkins picked up a slight knock but the big blow is Conor Hourihane who has been ruled out for a month due to a hamstring tear.
"It's a grade one tear, so it's best case scenario," added Johnson. "He was really surprised. He felt okay (on Tuesday). He's only had one injury in his career in pre-season so it's another young player who isn't used to injuries."
