Defending 139/5, Mumbai subdued Chennai to their lowest total in the current season, skittling them for a mere 79.
"It was a very important game for us coming today obviously coming after a loss, a very bad loss (against Hyderabad). With our win against Chennai who have been dominant will give us a lot of confidence going into our next phase of this tournament," Johnson said.
Johnson picked up three for 27 in his three overs and the Aussie would have dismissed his compatriot Michael Hussey but for three consecutive dropped catches by Kieron Pollard.
The left-arm seamer termed the dropped catches as bizarre, especially coming from a man of the West Indian's calibre.
"He has taken some unbelievable catches in his time tonight wasn't his night with catches. We all stuck with him, we stuck behind him. We played some tough cricket but that is just the way, the game goes," he said.