Ritchie de Laet slammed the defending which is ruining Pompey's season.
The Blues made it eight games without a win as they slumped to a poor 2-1 loss against Burnley last night.
More sloppy play at the back was behind the goals which condemned Steve Cotterill's men to defeat.
The loss means Pompey have now shipped a worrying 18 goals in the past seven matches.
They are also without a win at Fratton Park since October, while the last three points came at Norwich on December 11.
De Laet, on loan from Manchester United until the end of the season, insisted the individual errors had to be cut out if the Blues are to stop the rot.
The defender, who played left-back last night, said: 'They are easy goals we are giving away.
'The first goal, the player (Jay Rodriguez) creeps in and the second was a good overhead kick after a good save – but he (Steven Thompson) can't be allowed to do things like that.
'You can do what you want on the training field but you can't do anything about mistakes like that from us. It's just experience.
'We have to cut those mistakes out of our game if we want to start picking up wins.
'We are getting goals but then switching off again. We have to keep our concentration.
'They say you are vulnerable after goals but they are lapses in concentration and that's what is doing us.
'Jamie has made a good save for the second goal. It was a good goal but there were three players on the line. Someone's got to go for the ball.
'It's a lapse in thinking and concentration.
'It's worrying but going forward we look like scoring all the time.
'If we cut the mistakes out we'll get the results.
'You will concede goals from good play but since I've been here we haven't conceded a goal from dangerous play from the opposition – it's just mistakes that we make.'
De Laet has been impressed with Pompey's attacking quality since arriving from Manchester United.
But he was concerned by a tendency to resort to long balls he felt crept into their game against a Burnley side who picked up just their third away win in 35 fixtures.
De Laet said: 'We are good going forward.
'When we play football we are dangerous.
'King (Kanu), John Utaka and David Nugent are dangerous players.
'But sometimes we just kick it forward too easily.
'If you do that against the likes of defenders like Michael Duff and Clarke Carlisle, that's what they want.
'They will just head the ball away. It's an easy game for them.'