Mumbai, the most successful team in IPL history, chased 157 with eight balls to spare as captain Rohit Sharma hit 68.
Trent Boult took 3-30 for Mumbai, including Marcus Stoinis with the first ball of the match in Dubai.
Delhi were 22-3 before captain Shreyas Iyer made 65 not out – he added 96 with Rishabh Pant – but Mumbai ensured their total was never enough.
The defending champions were always in control of their chase after Rohit and Quinton de Kock plundered 45 from the first four overs.
Rohit was caught at deep mid-wicket with 20 needed from 23 balls and, although Kieron Pollard and Hardik Pandya soon followed, Ishan Kishan’s unbeaten 33 off 19 balls took Mumbai to victory.
It follows their IPL wins in 2013, 2015, 2017 and 2019 and means they have won the world’s premier domestic Twenty20 competition at least twice more than any other team.
This year’s tournament was held in the United Arab Emirates without fans and delayed from the spring because of the coronavirus pandemic.
England pace bowler Jofra Archer was named as the most valuable player. He took 20 wickets and scored 113 runs, including 10 sixes, for Rajasthan Royals.