Fletcher took his contribution to five goals in the last seven games since McCarthy challenged his ?7million record signing to justify his price tag.
The Scotland international only reclaimed his place after Kevin Doyle suffered a knee ligament injury six weeks ago.
Adlene Guedioura was also on target for Wolves while the visitors could only manage a Peter Odemwingie penalty in reply - his 15th goal of the campaign.
"He has scored some important goals and it is lovely to be proved right," said McCarthy. "I spent millions. He was my first choice. That is why I went and got him in the summer before I went on my holidays.
"I thought it was the best piece of business I could have done. I think he has proved to be exactly what I thought he would be. He was delighted with his goals and I am thrilled with him."
Source: PA
Source: PA