Wolves hit the woodwork three times in the opening stages of the game at Ewood Park.
McCarthy said: “We started the game really well as everyone knows who watched it and then defended badly.
“We just had a bad day defensively that’s for sure because we had chances. But that doesn’t matter when you’re three goals down.
“We conceded far too easy from a corner kick for the first and could have done better for the second.
“Paul Robinson made some cracking saves but we conceded another goal from a restart at a free kick and it’s poor defending on our part.”
McCarthy added: “You saw the start of the game and we didn’t hold back. Hit the inside of the post and another post so we started fairly brazen.
“But 2-0 down there’s hardly any point not having two strikers on.
“Sam will be delighted because they’ve got their just rewards but their just rewards have come from our poor defending.”
