Paul Cook felt Pompey lost their attacking confidence as they went down to Oxford.
And the Blues boss admitted his side didn’t look like scoring as they fell to a 1-0 loss to their promotion rivals.
After impressive recent form, it was a rare off day for Cook’s men against Michael Appleton’s side.
Oxford had the better of possession and carved out more chances in a game which was short on clear goalscoring opportunities.
Cook thought a bitty clash unfolded with Pompey short of their best on the front foot.
He said: ‘It was a bits and pieces game. There wasn’t much in it.
‘I didn’t think they offered much in the second half, I must admit.
‘You take the penalty away and their goal was a breakaway.
‘I thought we could manufacture a goal, but we didn’t really look like scoring.
‘It was a lacklustre performance from us.
‘Our attacking players looked flat.
‘You start looking at whether we can get Ben Tollitt and Kal Naismith on to liven it.
‘All of a sudden we were gambling rather than having confidence in what we were doing. It wasn’t there.
‘That comes from us as a squad and a team.’
Cook is hoping the loss acts as a wake-up call for his side with 20 games remaining.
Pompey have been steadily picking up points, but now find themselves seven points off the automatic promotion berths.
Cook knows there is still much to be done in reshaping his side.
He said: ‘I’m a realist.
‘We’re not just going to turn up Saturday and Tuesday and win games.
‘If that was the case I wouldn’t be at Portsmouth.
‘There’s a long way to go and I’ve got a difficult job to do.’
One major plus point for Pompey was the encouraging debut of keeper Ryan Fulton.
Fulton came straight into the starting XI after signing on loan from Liverpool until the end of the season.
That was with Brian Murphy missing through injury after a collision in the FA Cup win over Ipswich.
Fulton produced a sound showing on his Football League debut.
That was capped by his double save to deny Liam Sercombe after conceding a penalty in the second half.
Cook said: ‘Ryan’s done smashing.
‘It was a great game for him to make his debut.
‘It would have been great for him to save the penalty and for us to go on to win the game.
Unfortunately it wasn’t to be.’
– JORDAN CROSS