Hull were without newly-appointed skipper Gareth Ellis after he injured a foot in the warm-up, and although they battled to keep the Rhinos at bay for almost an hour, they finally buckled under the pressure of a second-half onslaught from the Super League champions.
"It was a tough one to start with and we knew it would be," McDermott said. "For 60 minutes it could have gone either way."
He went on: "Although it was 6-6 at half-time, I thought we were the more dominant team. But had Hull scored early in the second half it would really have been game on.
"I thought we were very good. They lost Gaz Ellis and it obviously affected them. As the end went on, our strike had a bearing on the game. You can't reach that level every week but you can maintain that effort."
Hull coach Peter Gentle, whose side scored an equalising try through debutant centre Joe Arundel, refused to use the loss of Ellis as an excuse for the defeat.
"It started bad and got worse," he said. "It's tough losing your leader like that but we're not going to use that as an excuse.
"At 6-6 I thought we were going okay but we fell apart in that second half.
"We started playing like individuals when Leeds went up a gear. It's a massive reality check for us, it shows how far we're off the top teams in this competition.
"We've a lot of work to do but I still believe we can get there. I don't think that's a fair indication of what we can do."
- Sports & Recreation
- Gareth Ellis