The 22-year-old winger came on for the last six minutes of England's 3-1 friendly win over Mexico as he bids to snatch a seat on the plane to the World Cup.
Johnson's England debut came less than six months after he moved from Middlesbrough to City in the January transfer window.
"It was brilliant and I really enjoyed it," he told City's official website. "The last six months have been unbelievable and winning my first England cap was the proudest moment of my career.
"I wasn't too nervous but deep down I was desperate to get on. It's what you dream of when you're a little lad and to make my debut in front of 88,000 people at Wembley is something I'll never forget."
Johnson faces an anxious wait to discover if he will make the 23-man squad, but is clearly still in Fabio Capello's thoughts as the manager prepares the final cuts.
"Middlesbrough were great for me and my development, but coming to City has been fantastic," Johnson added.
"If I'd stayed where I was I doubt I would have had this opportunity and now hopefully I can end the season by going to the World Cup."