The Robins came from a goal down to win a tricky game against Carlisle and keep themselves four points clear of Nottingham Forest.
"It's in our hands to clinch promotion with either a win next week or against Rotherham on the final day," said Johnson.
"This is a giant stride and will send shockwaves to our rivals.
"The supporters were magnificent and I'm glad two of the goals were right in front of them."