It was game full of drama in which both sides had a penalty saved and Leicester defender Paul Konchesky was sent-off for dangerous play after goals by David Nugent and his strike partner Jermaine Beckford had put the home side in command.
Harrison said: "It was a strange game. We had a good chance to score early on and for the first 15 minutes we did very well, but then we lost our way a bit.
"After they scored we climbed our way back in. We came up with a game-plan for the second half but then gave away a bad goal and that was the nail in the coffin, really.
"We had our chances but we didn't really defend well enough. We showed a bit of naivety and we have got to learn sooner, rather than later.
"A saving grace is that our attitude and application is very good. It is an important asset that we have remained enthusiastic and our chins haven't dropped."