Commonwealth Games light-heavyweight gold medallist Johnson proved too powerful for Belfast's Phillip Townley as he fought on the undercard of Ricky Burns' world title defence at the Braehead Arena in Glasgow.
Johnson, who was born and bred in Lincolnshire but fought for Scotland in Delhi courtesy of his Glaswegian grandparents, admitted he had followed his manager Naseem's advice.
"He just said 'knock him out, end the fight in two'," Johnson said.
And the former multiple world champion, who returned to boxing last month to take control of Johnson's career, was delighted with the response.
"It was a chilling performance, an absolutely brilliant performance," said Hamed.
"It looked like he had been in that ring as a professional for the past ten years.
"It was amazing - crisp shots, very confident. That guy had never been stopped.
"Callum just looked so slick and so ready. If it was up to me I would put him in for a title within ten fights because he's capable of winning any kind of title right now.
"It's all about how we're going to hold this guy back - you're looking at ten fights and ten knockouts.
"I can't say he's going to go up to six rounds or eight rounds because he's got dynamite in his hands."
Johnson's participation in Delhi was almost curtailed by a technicality as he fell months short of automatic qualification under rules that state an athlete must have represented Scotland for five years.
But his career has since taken off and Johnson, whose shorts encapsulated both the St George's and St Andrew's crosses, is loving every minute.
"It's good to get my debut out the way, I was a little bit nervous," the 25-year-old said.
"I represented Scotland in the Commonwealth Games, making my debut in front of all these people in Scotland, and to get a stoppage, I'm over the moon, I'm buzzing.
"I have been waiting for this since I was a boy when I first put the gloves on in the kitchen with my dad, I dreamt of turning professional and boxing in front of all these people.
"It's just happened, and happened in good style I thought."