"To be able to defend a score like this was a brilliant effort, I couldn't ask for more.
"When three overs were left, I had confidence in the bowlers ... it was about giving freedom to them because they're the masters and they've done it before. I just told them to do whatever they want and set the field accordingly," Rohit said.
Earlier, Krunal Pandya's 47 off 38 balls lifted Mumbai Indians after a collapse to 79-7 in the 15th over.
Jaydev Unadkat (2-19) rattled the top order with two early wickets and then Adam Zampa got the prized wickets of Rohit (24) and Kieron Pollard (7).
Unadkat took one of the finest catches in the IPL to dismiss Lendl Simmons when the ball stuck in his left hand fingers just above the ground as he dived full length off his follow through.
But Krunal kept his composure and added a vital 50 runs for the eighth wicket with Johnson before he fell off the last ball of the innings which gave Christian (2-34) his second wicket of the innings.
Supergiant looked to have the match in the bag until losing Mahendra Singh Dhoni in the 17th over and slipped to 98-3 as Jasprit Bumrah conceded only three runs.
Needing 30 off the last three overs, Lasith Malinga gave away only seven runs in the 18th before Smith hit Bumrah for a six in the next over and brought the target down to 11 off the last six balls.
But the pressure seemed to get to Supergiant in the last over as Tiwary holed out to long on and Smith threw away his wicket off the next ball while attempting to clear Ambati Rayudu at sweeper cover.
"It's a hard one to swallow. Just disappointing to lose, it wasn't the fairy tale finish we wanted," Smith said.
"They (Mumbai) were probably below par with 129, but it was a tough wicket to get runs, everyone could see that, just couldn't get over the line."
It was Mumbai Indians' first win against Supergiant this season after losing both its league matches and also the first qualifier. Mumbai Indians' earlier IPL titles came in 2013 and 2015.
-AP
