McCarthy made nine changes from the side which played Tottenham at the weekend but still felt there was enough quality on display to dispose of the League One outfit on Tuesday night.
Instead he had to bring on first-choice strikers Kevin Doyle and Steven Fletcher to rescue the tie with three goals between them in extra time.
Wolves had needed a penalty from Christophe Berra seven minutes from the end of normal time to bring them level after Lee Hughes had broken the deadlock.
McCarthy said: "If you are looking for positives, then Kevin and Steven provided them because they are top class, the pair of them.
"But Notts County were excellent and did to us what we did to Spurs for 75 minutes at the weekend.
"This time we got a penalty and the win seems a bit unjust on them. But I felt the same against Spurs."
McCarthy added: "I want to take nothing away from Notts County. They played well. But our performance was very poor.
"It was a Premier League team, no trialists, no youth teamers, and we ought to have been capable of playing better."
Notts County boss Craig Short admitted to being frustrated at the outcome.
He said: "We were leading 1-0 and had the chance to make it 2-0 and finish them off.
"I'm exceptionally proud of them. They are so disappointed. It was there for the taking.
"But I am proud of everyone of them."
Hughes displayed a T-shirt emblazoned with the words 'Boing, Boing' after opening the scoring - the chant of his former club West Brom.
It was his response to being booed and coming in for verbal abuse throughout from the Wolves fans.
Short said: "He expected abuse, it fired him up. He caused their centre-halfs so many problems."