Town fought back after conceding an early goal as DJ Campbell and Michael Chopra made it four wins from seven games since McCarthy took charge.
"I'm delighted with the win and I really wanted to win this game," said McCarthy.
"I thought that it was fairly even throughout and in the end that the three substitutes we brought on won it for us.
"There is a good spirit here now which wasn't here when I first came.
"There was a lot of finger pointing then but now we all seem to be pushing in the right direction.
"We're nowhere near to safety just yet though, and we just need to keep looking to pick up maximum points.
"I was really pleased for Michael (Chopra) because he has had some tough times.
"It was a great striker's goal and after all the hard work that he puts in he really deserved it."