The tricky Wolves winger failed to shine during a uneventful encounter at the City Ground in which both sides huffed and puffed but could not find the necessary quality required.
But with the game heading for a goalless draw, Kightly smashed home his eighth goal of the season and his first since the start of November to turn one point into three.
McCarthy said: "He's been getting a bit frustrated with himself (of late).
"I just said to 'Kights' that's not been his best performance. Arguably down in the lower end of his performances, but he stays on the pitch because he's a goal threat. He's got that quality and it's great when it pays off."
He added: "I wasn't really considering taking him off - leave him on, leave Sylvan on, change others. Chris (Iwelumo) scored last week but it didn't look like it was going to happen for him, he was having a big scrap with (Wes) Morgan and (Kelvin) Wilson. (Andy) Keogh came on and was lively, a threat. I'm fortunate I've got a good bench."