Argyle had sailed into a two goal half time lead against Steve Coppell's side only to be pegged back to 2-2 after the break.
"The players have let themselves down with their second-half performance and I'm disappointed for them as much as I am for the fans," he said after the 2-2 draw.
"We should have had three points tonight.
"We deserved a standing ovation at half-time and we deserved the silence we got at the final whistle. It wasn't for the lack of effort - lack of concentration has cost us.
"We knew there would be occasions in the game when we had to defend and, on the two occasions when they got their goals, we never defended as well as I would have liked."