In front of his excited home fans, the 28-year-old left-hander, one of the big gambles of the IPL auction when he was signed on a massive $1.78 million deal, had what he called an "absolutely incredible" experience at a packed Narendra Modi Stadium on Sunday.
It had all begun badly for the Aussie newcomer with Mumbai Indians trying to chase down Gujarat's 6-186.
He was introduced in the 10th over and was clouted in front of point for six first-ball by South African Dewald Brevis (46), before India captain Rohit Sharma (43) later welcomed him with two more boundaries.
In all he went for 17 off the over, and, looking a bit shell-shocked, it seemed it might be the last we would see of him with ball in hand.
But with the game in the balance - Mumbai still needing 27 off the last two overs with five wickets in hand - young captain Shubman Gill risked all by giving Spencer the formidable ask of bowling the penultimate six balls.
When the first got deposited for another six by Tilak Varma, it looked as if Johnson could end up the fall guy.
But he responded brilliantly, getting Varma caught in the deep next ball and then taking a caught-and-bowled off a mistimed pull by Gerald Coetzee at the end of an over which eventually went for just eight after the opening-ball maximum.
It swung the balance decisively towards the home side as Mumbai could eke out just 12 from Umesh Yadav's (2-31) equally nerveless last, two-wicket over, as the Titans squeezed home by six runs.
Johnson has followed up some of his heroics for the Heat in the BBL. (Dan Himbrechts/AAP PHOTOS)
"Absolutely incredible," beamed Johnson, who finished with 2-25 off his two contrasting overs. "To get the win is very special."
Of that 19th over, he added that the key was to persuade himself to "stay calm", with coach Ash Nehra telling him: "You're going to win this game."
"To have the backing from him and everyone else, even after going for runs in my first over, it's pretty cool.
"This is easily the biggest crowd I've played in front of, I've always wanted to play cricket in india - and here I am. I hope we can keep winning."
He had special praise for Gill, who's been given the captaincy at just 24.
"Shubman is unbelievable. He sat next to me on the bus trip, he was calming me. We talked through the game. As a young captain, he's unbelievable," said Johnson, who made a similarly special debut when he starred for the Oval Invincibles in The Hundred last year.
But it wasn't a happy return to his old stamping ground for Hardik Pandya, captain of the Titans in the previous two seasons, who smacked 11 off four balls before being caught on the boundary in Yadav's death over.
Earlier in Mumbai's innings, Aussie big-hitter Tim David had made 11 off 10 balls before being caught brilliantly by a diving David Miller running in from deep midwicket off the excellent Mohit Sharma (2-32).
