Stephen Ward's winner gave Wolves a 2-1 victory, lashing home a left-foot shot in the 48th minute when Paul Robinson saved Kevin Doyle's penalty after Stephen Fletcher had swiftly equalised a debut goal by Mauro Formica in the first half.
But McCarthy singled out commanding debutant Johnson for praise, saying: "Roger has certainly added a great deal to the back four. I'm delighted with all of them [the new arrivals]. It was a great start."
Having watched his side secure survival on the last day of last season, McCarthy admitted it was a major boost to get the new campaign up and running with a win.
McCarthy added: "You can't ask for much more than that. It's normal that if you go behind in the Premier League you don't come back - especially away from home.
"The first bit of quality we produced was for our equaliser and the game was end to end in the first half. But in the second half I thought we controlled it for the most part.
"It can be nervy for the home side on their home debut but it's up to the opposition to take advantage of that and I think we did that.
"It's our third year in the Premier League now. The players we have brought in have added something to it and those who have been here two years have got better. It's one down and 37 to go."
Blackburn boss Steve Kean admitted his club need to bring new faces in fast if they are to avoid a repeat of last season's relegation near-miss. Kean was forced to throw Steven Nzonzi back into an unfamiliar central defensive role and his personnel problems were further complicated by a hamstring injury to Brett Emerton.
Kean admitted: "We're in a position where 11 players have left and only three have come in. We have to bring players in in order to have a competitive squad. We've got four bids out there at the moment and we have to irritate those bids and make sure they formalise into full signings. If not we're thin on the ground."
Source: PA
Source: PA