The Gulls overcame a huge hurdle when they recovered from losing Koue Niate early to win 2-0.
Playing a man short since the 13th minute, they scored twice through Jamie Reid to take the points.
It closed the gap on leaders Woking and avoided a sticky situation on what eventually turned out to be a fantastic day.
"To go an man down so early and beat a decent team on a good run was really something,” said boss Johnson to DevonLive.
"We were against a strong wind at the time and we had to get a good shape to cope with things. To get a goal before half-time was a real boost.
“When you have to trust your training' and we asked them all to give an extra 10 per cent to alleviate being a man down. They did that.
“We restricted Dartford to very few chances, we also saw the game out very well after the second goal and we can all be very proud of our football club.
“Woking did well to get back to 3-3 from 3-1 down, but it was all about us today because we could easily have ended up four points behind them.
"It’s going to be a very interesting end to the season."