The makeshift central defender earned his marching orders in the 67th minute of Sunday’s 1-0 defeat at Sunderland.
Having been dispossessed by Wilson Isidor high up the pitch as last man, the Blues skipper responded by pulling back the attacker as he attempted to burst past him.
Mousinho, who afterwards agreed with referee Thomas Bramall’s decision to send off the 33-year-old, subsequently introduced new signing Rob Atkinson off the bench to partner Ryley Towler at centre-half.
And he had sympathy for Pack, who has now started 10 successive games in a role he had never previously featured in.
The Blues head coach told The News: ‘I thought it was a red, no complaints.
‘Marlon was really good (against Sunderland) – obviously apart from the moment where he ends up getting sent off – but it wasn’t a defensive issue or any glaring deficiency in his game, it was just the fact he made the wrong decision.
‘He knows that and he’s put his hands up for that and apologised to everyone in there. He’s a really honest lad and that’s all you can do.
‘Since he moved back there, we’ve had some real success in some of the performances and I think he’s played really well and has played his part.
‘He moved back there for the Preston game and, at that point, we’d only won one game all season. Now we’re sitting in a much better position.
‘We are not in the position we want to be in, but we are sitting in a much healthier position than we were back then.’
Pack was pressed into centre-half duties at the start of November, following Tom McIntyre’s loss of form, Regan Poole’s latest injury set-back, and the on-going absences of Conor Shaughnessy and Ibane Bowat.
The League One title-winning skipper had previously lost his place in the centre of midfield to Andre Dozzell, having been a regular start in the opening two-and-a-half months of the campaign.
Regardless, the Blues turned to the Buckland boy as a last resort at centre-back – and, as ever, he has demonstrated his unflinching commitment to the club by dropping in there.
Mousinho added: ‘We are keeping more clean sheets, we are causing sides a lot of problems at home, in particular, and then away from home, also causing teams issues.
‘So I think Marlon has been really good.’
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