But the Blues boss took solace from his side finding a way to win against the Cumbrians at Fratton Park, despite being well short of their best.
Mousinho passed up a stack of first-half chances in the eventual 1-0 wins, failing to hit the back of the net from 13 shots on goal.
Colby Bishop was surprisingly the chief culprit, with the Magic Man missing one gilt-edged chance amid a few opportunities.
Mousinho stated he had no issue at all with his players not being able to make more of their efforts, however.
He said: ‘I think we were a bit wasteful in the first half, but I haven’t got a problem with that.
‘We’re not going to be able to hit the back of the net every time and that’s okay.
‘Honestly, I haven’t got a problem with that because we created and I think I’ve been consistent with that: if we are creating chances I haven’t got an issue because I know we are going to put the ball in the back of the net more often than not.
‘It’s when we drifted into periods of the second half where we didn’t create (there’s an issue). I thought we were just a bit open and had a defensive unit and attacking unit without linking them too well.
‘It’s hard to assess sometimes when you’re on the sideline, but we know we can play better than that.’
The game’s defining moment arrived in stoppage time, with Conor Shaughnessy once again the late hero - echoing his header against Wycombe earlier this month.
Mousinho added: ‘We say we keep finding a way, but if we compare the Wycombe game and this one they are complete contrasts.
‘I thought we pretty much controlled the Wycombe game from start to finish and was really pleased with that. We totally deserved that, but it was completely different this time. We found a way, but found a way without playing particularly well. I think that’s the first time we’ve done that this season,
‘When the dust settles I think I’ll be very pleased we managed to do that. We’re not going to be sparking for 46 games. Hopefully we are for the majority of them, but there will be days like these. If you can come away with the win that’s a brilliant spot to be in.’