The 25-year-old struck the only goal against Leeds two minutes after his introduction to restore Cardiff's 10-point lead at the top of the Championship.
And Campbell, whose three-and-a-half-year stay at Sunderland was severely disrupted by a serious knee injury, is delighted to be back and scoring goals.
"Being injured for such a long period put me back a couple of years," he told Wales Online. "But now I am as sharp as ever, as fit as ever, and want to push on in the next couple of months.
"It's the best I've felt in a long time, when you first come back you get aches and pains in your calf because it's not been used to running about.
"But it's been brilliant for the last few months and I'm ready to play and score goals.
"There were times when it crossed my mind whether I would play again, you do get down days."
Campbell returns to his native Huddersfield on Saturday as Cardiff look for yet another victory.
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