Wigan Athletic 'smelt the fear' on my players - Huddersfield Town chief
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Pelach took temporary charge after the sacking of Mark Fotheringham in midweek, but he was unable to prevent the Terriers dropping to second bottom of the table - ahead of Blackpool only on goal difference.
"It was a mental thing, everything is about the mind nowadays," he said.
"The circumstances of the situation didn't help - they were playing at home, and you can expect the home team is going to push towards the end.
"They could smell that we were not in a good moment, they were clever and they pushed us back.
"We tried to defend what we had, because we didn't have any counter attacks or possession.
"They did well, they smelt that we were not good, and it is our fault, we shouldn't drop back like that.
"It is a confidence thing."
Pelach thought it was very much a game of two halves.
"In the first half, we showed what we wanted to do, I think the team was understanding well, and showing balance," he said.
"In the second half, it was the same for the first 10 minutes, but then we disappeared completely.
"We need to understand why that happened, because we need to improve and we need to do it quickly.
"We disappeared in terms of having the ball.
"If they counter-press you with intensity, you have the option to play long and put them on the back foot.
"But we stopped giving the solutions we were showing in the first half, with the ball.
"Without the ball, we also lost control, and I am not happy with what happened in the second half.
"We lost the goal from a corner, and that can happen, it's not down to tactics.
"But we cannot let this happen, the way we lost control in the second half."