Micky Adams was critical of Port Vale after they failed to make their numerical advantage count in their 2-0 defeat to Preston.
North End were reduced to 10 men in the 13th minute when Neil Kilkenny was mistakenly sent off.
Joe Garner was the Preston player who should have seen red after he clashed with Anthony Griffith and he ensured the referee's decision came back to haunt Vale. He fired Preston ahead in the 30th minute and then converted a 71st-minute penalty to secure all three points for 10-man Preston.
"I'm very disappointed because when a side go down to 10 men so early on you have to ask questions why you haven't beaten them," said Adams.
"We didn't win because we were lethargic in the first half, didn't get the ball wide early enough and played too many long straight balls.
"But we've also got to give credit to Preston. They are a good side who won at the league leaders Leyton Orient and now they've won their last three away games without conceding a goal.
"It was always going to be a test for us but we've failed it because Preston have put bodies on the line and we haven't been good enough to break them down."