Paul Cook hailed a ‘big three points’ as Pompey powered past nine-man Mansfield Town 4-0 to climb to fourth in the League Two table.
The Blues led after just 11 minutes when Gary Roberts netted from the penalty spot.
Second-half dismissals of Kyle Howkins and Stags substitute Alex Iacovitti then turned the game firmly in the home side’s favour.
And Noel Hunt climbed off the bench to net his first Blues goal late on, with Carl Baker’s last-gasp double putting the seal on a resounding victory, as Pompey responded to two successive league defeats at home.
The Fratton fans voiced their frustration at times, however, after the interval as Pompey went in search of the game-clinching second goal.
But after acknowledging anxiety had crept into his side’s play, Cook vowed to work on the Blues’ identity after securing a crucial and hard-fought victory.
He said: ‘It was a big three points.
‘After all of the Checkatrade Trophy games, we have won on the Saturday, which is quite an interesting stat.
‘We knew today was a difficult test - Mansfield are a good side and have got some very good players.
‘There are no easy games in this league.
‘The days when you turned up and just rolled teams over are well gone now.
‘Teams are very well set up - they are organised with fitness and sport science.
‘Today you can see within our lads anxiety creeping into our play.
‘I have got to make sure our lads become themselves and their identity becomes strong and good and we can achieve everything I believe we can.’