The Airlie Birds triumphed 46-20 at St James’ Park on Saturday afternoon, and McCarthy felt that they wasted too much energy by their ineptitude in possession.
“It was a pretty tough result,” he said.
“Obviously I think we were second best on every front today.
“It’s pretty disappointing when you’re in a special event like this, and in the derby.
“We just need to assess what we’re doing wrong.
“In the last couple of weeks we’ve struggled keeping hold of the ball, and that’s taken juice out of our defence.”