Both teams are searching of their first win of the competition, having lost both their respective games so far.
In three matches with Gujarat Lions last season, Roy scored 59 runs; on Saturday, he needed only 33 balls to better that tally.
Both the batsman cleared the boundary ropes easily as runs began to flow thick and fast.
Rahul Tewatia, Trent Boult, Daniel Christian and Mohammed Shami may have been expensive, but with each of the bowlers taking crucial wickets, Delhi were able to restrict the hosts.
Mumbai raced to 50 runs in just 3.4 overs, as Yadav and Lewis continued their onslaught on Delhi bowlers. He first bowled his stock ball and then a googly to trap Saha leg before. The highlight of his assault was a reverse swept six as Mumbai muscled their way to 144 for 2 after 13 overs. Spinner Rahul Tewatia applied the brakes and send Lewis back, who was caught by Jason Roy at mid-off. Strategic timeout! 5:08pm: Mumbai Indians 158/2 after 15 overs Kishan smashes two boundaries to Shami, nine runs off the over.
This, perhaps, could be a front-loaded blueprint for the rest of their season, with perhaps Morris held back for the slog overs; and Gambhir playing the role of a firefighting No. 4 or No. 5 in case Daredevils lose early wickets, and remaining happy not to get a hit if the power-hitters really get going.
He, along with Evin Lewis, hammered the bowlers all around the park to make the highest powerplay score in this edition of the league. But Gambhir (15), failed to convert his start, as he gave a sitter to Rohit Sharma off Rahman.
Bowling: HH Pandya 2-0-32-0, Dananjaya 4-0-47-0, Bumrah 4-0-27-0, Rahman 4-0-25-1, Markande 3-0-42-0, KH Pandya 3-0-21-2. Four runs off the over.
Pant did not spare Dhananjaya, hitting him for two sixes and a four as Delhi grabbed 19 runs of the tenth over. Mumbai have lost two excruciatingly tight games, one of which they had no business losing.
Under the cosh now, the three-time victor - which has been forced to make a few changes because of an ankle-related injury to all-rounder Hardik Pandya and the non-availability of Australian fast bowler Pat Cummins - is hopeful of fielding its best eleven against the Daredevils.
The last over was heart-stopping with Delhi needing 11 to win and getting 10 following a four and a six off Mustafizur Rehman by Roy off the first two balls.