Johansen was on target at St Mirren Park with a late penalty, won by James Forrest, who opened the scoring for Celtic on 63 minutes.
The Buddies had defended in depth for the first hour of the match and frustrated the visitors, but the outcome was never in doubt following the opening goal.
And with nine matches remaining Celtic are now eight points clear of Aberdeen at the top of the Scottish Premiership.
“It looks great for us now. It’s nine games left in the league and it’s going to be difficult to take us now,” Johansen said.
“This was another important win and we just need to keep focusing now on every game over the next couple of weeks.
“I don’t think we’re unbeatable but you can say there is a huge confidence in the team now.
“I think we are starting to look fitter and we have much more of the ball because we are playing with a higher tempo and that’s the way the manager wants us to play.”
While Celtic found it hard to get their rhythm going in Paisley, Johansen feels St Mirren deserve credit for their disciplined performance.
But the 24-year-old was happy to get the three points following the international break.
Johansen said: “Some of the guys have had a few days off and some of the guys were away with the international teams so it was good to be back together and be prepared for the rest of the season.
“St Mirren frustrated us for a while. They played well, especially in the first half and credit to them for that.
“But we know that we had the ball so much that they would need to run. It was going to be difficult for them over 90 minutes so we knew it would open up.”