Steve Davis blamed defensive lapses of concentration as Crewe surrendered a lead to lose 2-1 against Leyton Orient.
Debutant Chris Dagnall fired the O's back to the summit of League One when he netted twice inside seven second-half minutes.
Alex fans were daring to dream of a shock victory, but their hopes lasted for only eight minutes after Byron Moore's far-post finish handed Davis' struggling side a deserved advantage.
"The game could have gone either way but swung Orient's because of a couple of errors at the back," said the Crewe boss.
"We couldn't build on our lead and one or two of the players seem to get nervous in those situations.
"Why? I don't know. Maybe it's the realisation of being one-up against a decent side and having to hang on.
"And it comes down to the ability of the defenders to do their jobs. No-one is cutting us open or showing particularly fancy football. But it's always our mistakes and our switching off and they've all got to be accountable for that.
"Individual errors do cost you against the top teams.
"I thought Orient looked very ordinary and I thought we competed very well. But yes they have got good players which is why they are in the league.
"They were very clinical in their finishing and obviously Dagnall has done that before at this level."