Johnson reserved special praise for young striker Danny Philliskirk, who has scored five goals in this season's competition.
Johnson said: "It was an excellent performance and I'm really pleased with the manner of the win.
"After starting the game well we eased off slightly, but once we got going we stayed relentless.
"Some of our football was excellent and so was our finishing. We kept our heads around the box instead of blazing at chances.
"Danny Philliskirk in particular was fantastic. He is a technician who is gaining an extra edge to his game with the more experience he gets."
Johnson had some sympathy for red-carded debutant Jordan Bove, adding: "I've given him the 'midget hairdryer', but he isn't a bad kid.
"He got too excited on his debut and it was a bad tackle. We'll put it down to youthful enthusiasm."