While Royals shrugged off a middle-order fumbling, it turned out to be a disappointing day for Mumbai Indians.
Earlier, sent in to bat, the returning Rohit got Mumbai off to a rollicking start along with de Kock.
Rahane further flexed his muscles when he hacked Joseph for two fours and a six in one over and did not even spare Jasprit Bumrah as Rajasthan accumulated 59 runs in the first six overs without losing a wicket.
Buttler scored 28 runs in the 13th over, hitting four fours and two sixes off West Indian seamer Alzarri Joseph, as Rajasthan chased 188 for victory.
Playing probably one of the best knocks of his IPL career, stand-in captain Kieron Pollard promoted himself to number four and smashed 83 from just 31 deliveries which included three fours and 10 sixes.
Mumbai took a time-out to gather their thoughts after the Power Play and the move worked wonders with Rahane falling just second ball after the break top-edging Krunal Pandya to Suryakumar to deep square leg.
Batsmen: Jos Buttler has tapered off this week, but he faces his former side at Wankhede and would want to make a big statement before he jets off to England for World Cup preparations.
Mumbai Indians will take on Rajasthan Royals in the IPL T20 game on April 13 in Mumbai.
However, just when it looked like Rohit and de Kock complete a hundred-run partnership, Jofra Archer dismissed the former for 47 to give RR a much-needed breakthrough.
Mumbai lost a bit of their way post Rohit's dismissal with the new batsmen finding it tough to hit their straps right away. He was eventually dismissed for 89, holing out to Suryakumar Yadav at long-off.
Stokes and Archer picked 2 wickets each. Since the departure of Rohit Sharma, de Kock continued with his aggressive style of play but wickets kept tumbling from the other end. Against Mumbai Indians on Saturday, however, Buttler grew in confidence in the middle, and unleashed a fierce array of strokes towards the latter half of his innings to hasten RR's run chase.