Guy Whittingham bemoaned Pompey’s sloppy opening after their 1-0 defeat at Oldham.
The Blues’ extended their winless run to 22 matches as Jose Baxter’s 11-minute goal proved decisive.
That strike - which saw a costly error from keeper Simon Eastwood - followed a poor start from the visitors.
Pompey picked up in the latter stages of the first half, with John Akinde having their best chance.
Sam Sodje was then shown a red card for violent conduct in the 50th minute.
But Whittingham felt it was Pompey’s tough opening which proved their undoing.
The caretaker boss said: ‘In general, I was pleased with the way we handled ourselves in the second half but I was disappointed that when we did get the ball, we didn’t put it in the right areas.
‘But I felt we made a poor start. We knew if we gave them time on the ball, they would put quality balls into the box.
‘We knew we wanted to put pressure on the ball. Until the goal went in, we didn’t do that.
‘Suddenly the goal went in and they remembered what they had to do.
‘The first 10 minutes has cost us and obviously the sending off. I didn’t see the incident but we will have a look at the DVD.’