Ronald Zubar played Raul Meireles onside by dropping too deep and Fernando Torres scored the first of his two goals, while Meireles also found the net.
McCarthy said: "I think we let them off the hook by trying to play offside after 30-odd minutes. We then got done by a wonder-strike which no-one is stopping - you could have put two goalkeepers in.
"The third one is incidental because the game was finished - two mistakes and a wonder strike."
McCarthy felt Kenny Dalglish's return to the dugout a fortnight ago has had a major influence on Liverpool, although he expressed his sympathy for predecessor Roy Hodgson.
He said: "We beat them when Roy was there. He is such a great guy and a top coach but it is Kenny Dalglish coming out of the stand.
"I think he is enjoying a support and a warmth Roy didn't. He has garnered and nurtured that and they are on a better roll than they were because of it."
Source: PA
Source: PA