It ended a concerning run of successive goalless draws in style, with Colby Bishop, Abu Kamara and Regan Poole all netting in the success.
Certainly a timely result and performance heading into the international break – and Mousinho was rightly delighted with the Fratton Park outcome.
He told The News: ‘The important thing is the result first and foremost – and the performance was outstanding.
‘Certainly we were outstanding for 70 minutes after a bit of an indifferent start. I didn’t think we were terrible, but they caught us on the break and scored a decent-enough goal.
‘Our reaction after that was excellent, from thereon we looked the better side throughout, particularly in the second half, I thought we were excellent. A couple of players got their second wind and it was relentless kicking into the Fratton End.
‘It has been no secret, we speak about this in the press, we speak about it after games, we want to try to score more goals.
‘One of the things we’ve spoken about this week is we didn’t necessarily feel we weren't scoring because of how defensive we had been - we just needed a bit more creativity going forward and a bit more quality in some of those moments.
‘We got that against Peterborough and that was achieved with trying to be expansive in terms of the way we were playing.
‘It was thoroughly, thoroughly deserved. We didn't look threatened at all until we went down to 10 men, so performance-wise we are really, really happy.’
Mousinho also felt the Blues could have added to their goal tally, particularly in the second half before reduced to 10 men.
He added: ‘Probably the only slight part I’d look at was that, if we can keep improving, putting those games to bed.
‘We had chance after chance, a few goalmouth scrambles, their goalkeeper made a couple of great saves, particularly on the near post to Abu’s shot, we hit the bar, there were loads of set-pieces.
‘Once we nail that down we will be a bit more ruthless.’