A Wayne Rooney penalty and a Nemanja Vidic header gave United a 2-0 halftime lead against a Wolves line-up showing 10 changes to the side that beat Tottenham Hotspur 1-0 on Saturday.
Antonio Valencia added a third goal in a pedestrian second half to put United joint top of the Premier League with 37 points, although Chelsea, who have a better goal difference, can restore their three-point lead against Portsmouth on Wednesday.
Premier League rules state that teams must play a full-strength side in every game, although a spokesman said it was unlikely that Wolves would suffer any punishment for a team selection that appeared designed to rest the first-choice side for Sunday's match against Burnley.
"We've just got a really busy period coming up," McCarthy told BBC Radio Five. "They were all first-team squad players who played tonight, not reserves and I have to say there were some really good performances.
"That team did as well as we did against Arsenal and Chelsea."
After holding United at bay for 20 minutes and even having a glorious chance volleyed over by George Friend, Wolves slipped away quietly once Rooney had tucked away his 12th league goal of the season following Ronald Zubar's needless handball.
"It's been a great few days," manager Martin O'Neill told the BBC. "I was worried about this fixture but confidence is high and when confidence is high you can perform."
