Warburton said: “I’m disappointed with the level of performance. We felt well prepared, we knew there would be a good atmosphere and we knew what they would do.
“But we weren’t good enough. There is no point going in there and saying we were okay here and there.
“No, we weren’t good enough as a group. You can mask over it and say we should have had the offside goal and they cleared one off the line.
“No and to concede to two tap-ins at the far post is unacceptable to us as a group.”
Warburton didn’t try to use a strike from Joe Dodoo which was chalked-off for offiside against Harry Forrester as an excuse, but did admit to being irked at the decision to deny his troops an equaliser.
He said: “We were unhappy. I think Harry is offside, if you analyse and scrutinise it.
“But the fact is the goal was given. The flag didn’t go up and the linesman was the last man in line. The flag didn’t go up for 14 seconds. He took five or six paces down the touchline.
“What happened to change the minds?
“It’s not clutching at straws, or being sore losers. It makes the game 1-1 and it’s a big turning point.
“We are bemused. The boys were celebrating with the fans. Thirteen or 14 seconds go by and then the flag goes up. We asked the fourth official why and I was told they were deliberating the decision.
“In my mind, and as the delegate confirmed, it’s either instantaneous he’s offside or he’s not.
“I think Harry was, but it wasn’t given for too long a period.”
“What we have to do is respond very positively. We have got to have a good response. There is no feeling sorry for ourselves.”