However, McDermott feels that the game could have been different had his team been given a spot kick before Newcastle bagged their second.
"Their [first] goal, from their point of view, was a little bit of quality on the left-hand side and maybe we needed to do better in that situation, but it was a good header, and their second goal was a great finish," McDermott told reporters.
"Having said that, at 1-0 Matt Smith was bundled over in the penalty area and I think because he is a big lad, the ref didn't give it. But it was a certain penalty, there's no doubt about that."
Newcastle will host Manchester City in the fourth round of the competition.