In a game twice interrupted by rain, Gujarat won on the DLS method off the final ball of what was effectively a super over, reaching the revised target of 147 for the loss of seven wickets.
Mumbai had been restricted to 8-155 after losing five wickets for 27 runs in the middle overs.
Will Jacks top-scored with 53 after being dropped before he had scored. Suryakumar Yadav was also reprieved on 10 before scoring 35.
When rain first intruded, Gujarat were eight runs ahead on DLS, but Mumbai stormed back through their pace bowlers when play resumed.
Gujarat lost four wickets in 16 balls as Jasprit Bumrah clean-bowled Shubman Gill (43) and Shahrukh Khan (6) to finish with 2-19.
Sherfane Rutherford smashed a quickfire 28 off 15 balls, but Trent Boult trapped him lbw and Rashid Khan also fell leg before to Ashwani Kumar's searing yorker, before rain took the players off again.
When play resumed well past midnight, the Titans were tasked with 15 runs to win and six balls in which to get them.
Rahul Tewatia smashed Deepak Chahar for a straight boundary off the first ball and Gerald Coetzee smacked a six over long off to bring down the target to four off three balls.
After Chahar bowled a no-ball, Coetzee holed out at mid-wicket, leaving the equation one from one, or a real super over contest would ensue.
Arshad Khan drove to Hardik Pandya at mid-off and scrambled home when he would have been run out with a direct hit.
"There was a little bit of chaos when we came in to bat after the rain," Gujarat captain Gill said. "But it's always good to have a W after the match."
Gujarat lead the standings with 16 points ahead of Royal Challengers Bangalore on net run-rate. Mumbai are in the fourth and final play-off spot with 14 points.
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