As well as satisfaction, Johnston would have been forgiven for feeling some surprise, given the result remained a mystery until she rose from her prone position. She knew she had shot well but had no clue if it was enough to take gold.
"All I knew was what I was doing. There are shooters that will get up and scan the scores from time to time. But, for the most part, all you can do is put in your best performance, and if it's good enough then it's good enough."
It certainly was today, overcoming a challenging wind and a pair of opponents who finished within 1.2 points of her 620.7 total. Even though she said it took time to hit her stride, Johnston led the 60-shot event early and kept hitting the target to hold off her challengers and continue this country's proud tradition in the sport.
"Once I figured out roughly what I wanted to shoot on, it was just all about concentrating on good aim, firing some good shots and hoping they ended up in the middle. Luckily, for me, most of them did.
"It's great to show people that New Zealand's still got it when it comes to shooting talent. We've had a few changes in the team but it's great to know we've got the depth of talent there to come in and perform on the Commonwealth stage."
Johnstone will get another chance to do that tomorrow, when she contests the smallbore rifle. While backing up the day after the highlight of her career precluded a big night of celebration, Johnstone thought it would have no other ramifications.
"Every match is a new match and it requires your focus and effort. Gold today is absolutely awesome but I don't know if it necessarily helps or hinders tomorrow. That's a whole new match. It's just about putting in my best on the day and seeing what happens."
That same approach has guided Johnston through a 30-year career in shooting, having followed in her parents' footsteps at the age of 15, and she planned on retaining it for the next Games.
"I thought about it for a little while before these Games and I'm quite keen to go to the Gold Coast and see what I can do there. Go for back-to-back."