The 2-0 win against The Saints was City's seventh win in eight starts and took them to within one point of a sixth position play-off place in the Championship table.
"Southampton put us under pressure in the second half and all credit to them for that," Johnson said after the match at Ashton Gate.
"But we defended when we had to and earned our win.
"Things are going very well for us and we are confident about making the play-offs, not in an arrogant way, but because we have faith in one another."