The Blues turned in a scintillating first-half display to head in at the interval leading Barnsley 3-0, through goals from Colby Bishop, Paddy Lane and Connor Ogilvie.
After the break, the Tykes found back to reduce the scoreline to 3-2 with 13 minutes remaining, setting up a tense finale.
Yet Mousinho’s men stood firm as victory made it 19 league games undefeated – and took them to the top of the table.
Certainly it was an eye-catching result, particularly the manner of a first half display which the head coach hailed as the best 45 minutes of his tenure.
Mousinho told The News: ‘I think it sends a powerful statement to the rest of the league – although a more powerful statement would have been a nice clean sheet in the second half!
‘For us it’s just about doing our job, getting on with it and making sure that we tick off the next box.
‘On Saturday we went away to a top side in the league and I thought we largely dominated proceedings.
‘We’ve now come away to a top side, completely dominated proceedings for 45 minutes and won the game – that is the difference between Saturday and Tuesday.
‘It was superb in the first half, the best we have played for 45 minutes since I’ve been here.
‘We put Barnsley to the sword in the first half, we were excellent, we looked lively, we looked bright, we looked front footed, and were very, very aggressive in the press.
‘The only downside was we didn’t go in at half-time four or five up, that would have made things a bit more comfortable.
‘The second half was flipped on its head and it was very tense towards the end. We saw the game out in the last 10 minutes really well, but prior to that did some really, really strange things and a lot to improve upon.
‘We’re not quite the finished article, we would have loved to have come away with a comfortable second half, but the most important thing was to win the game and the second was the performance.
‘We won the game and large elements of the performance were good.’
The 3-2 triumph, coupled with Exeter not in league action and Port Vale’s 3-2 home loss to Burton, catapulted the Blues to the top of the table.
It represents the first time they have led League One since August 27, 2022, following a 1-0 win at Port Vale.
Mousinho added: ‘Being top of the league is really pleasing, an added bonus.
‘It's nice to be there and we can work from that and take a lot of pride in the way we’ve got there.
‘It’s a culmination of a lot of hard work. These nights and results are evident of that, when you do the right things you do end up in a good position.’