Ben Close has urged Pompey to retain their belief following a narrow League One loss to Doncaster.
Reece James struck in the closing stages at Fratton Park to ensure the visitors claimed all three points.
But the Blues did improve as the contest progressed and enjoyed plenty of possession in the opposition half.
With tough away games at Gillingham and Sunderland approaching, Close knows they cannot afford to dwell on defeat.
He said: “It was frustrating and obviously not what we wanted. You don’t want to be losing any game, but especially at home.
“Doncaster defended solidly, but we didn’t create enough chances and that’s something we have to improve.
"You can’t get too down about it and have to learn from those matches when you don’t quite get it right."
“At times we played well and although that’s not enough, we’re still early in the season and there’s a big week ahead.
“You can’t get too down about it and have to learn from those matches when you don’t quite get it right.
“We’ll also take forward the positives, keep our heads up and look to put it right. We have to stay confident.
“There’s a chance to get over it quite quickly with two big away games approaching in the week ahead.”
Close was making his first league start of the season and was not used in either leg of the play-offs at the end of last term.
He said: “I’m extremely pleased to be back in the team and now I’ve got to work hard to try to keep my place.
“The games before are in the past and I can’t be concerned about them – I’m just looking ahead and trying to improve.”