The visitors held out for 84 minutes at the City Ground, before being breached by a deflected strike from Lewis McGugan.
McCarthy feels there are plenty of positives for his side to take out of the tie, despite another defeat leaving them in trouble, with it his opinion that key decisions could have gone their way on another night.
He said: "They're brilliant, they're a great bunch, they really are fabulous. I was really proud of the way they went about their job.
"We were unlucky not to hold out. It's a deflection that's cost us - they didn't look like they were going to get it any other way."
On the two dismissals, which saw Lee Martin and Richard Stearman given their marching orders, the former Ireland manager added: "Lee Martin - no arguments about that. As he (Henri Lansbury) has tackled him, he's knelt him, he's stood on him but, still, it's the one who retaliates always gets it (the red card).
"Second one - I don't know. At the time I thought he was going to book him, then I've just looked at it and he just seems to have shoved him (Andy Reid) off the pitch. If somebody shows me an angle where he's hit him in the face then he deserves it, but I can't see that.
"The first one I've no arguments with and, maybe, Stears just doing it having been booked already was a bit reckless on his part."