Buttler's 37-ball 77, laced with seven fours and five huge sixes and Rana's unbeaten 31-ball 54, comprising seven mammoth punches over the rope, outshone South African star Hashim Amla's maiden T20 century for Kings XI, as the visitors overhauled the massive target of 199, with more than four overs to spare.
Chasing a mammoth 199, the opening duo of Parthiv Patel (37) and Buttler dealt mostly in boundaries to raise Mumbai's highest first wicket stand of all IPL seasons of 81 runs, as the Punjab bowlers had little to counter the left-right pair.
Buttler started the onslaught from the very first over dispatching medium pacer Sandeep Sharma for a six before lofting him for another in his next over as Mumbai raced to 50 in just four overs.
Medium pacer Mohit Sharma was at the receiving end in his very first over, when Buttler milked him for three consecutive boundaries after Parthiv got one off the first ball.
The diminutive Patel was not too far behind and joined the party by cracking Ishant Sharma for a four and then a huge six off the legs before welcoming Marcus Stoinis with another huge six over deep midwicket.
Stonis, however got the better of the southpaw off a slower ball when Parthiv, who faced 18 balls and struck four boundaries and two sixes, failed to time it properly and ended in the hands of Glenn Maxwell at mid off.
Such was the carnage from the Mumbai duo that there were only five dots in the powerplay, including the wicket ball of Parthiv and more importantly included 14 boundaries.
Buttler, who had faced 23 balls by now, got to his fifty with a single to the right of long-on as Rana took the onus of getting the big shots.
The fall of the Gujarat wicketkeeper-batsman did not deter the visitors from scoring freely and No.3 Nitish Rana continued his great run with the willow to get his fourth half century of the season off 29 balls.
Rana started by launching Stoinis for a maximum before taking the likes of Ishant, Axar Patel and Swapnil Singh to the cleaners to take Mumbai to 123/1 midway into their innings.
Rana dominated the 85-run second wicket stand with Buttler, who was undone by Mohit's slower delivery with Mumbai within sniffing distance of victory.
Thereafter, Hardik Pandya struck a four and a six in his 4-ball 15 before Rana pulled Mohit over the long leg boundary for a six to seal the deal in the visitors' favour.
Kings XI bowlers could only blame themselves for letting the opportunity slip as none of the them had an economy rate of less than 10 runs an over.
Earlier, the hosts were off to a steady start with Amla (104 not out) and Shaun Marsh (26) putting on 46 runs before Maxwell took just one over from pacer Mitchell McClenaghan, milking 28 runs, to change the complexion of their innings.
McClenaghan's over, the 15th of the innings, was incidentally the second-most expensive over of this IPL season.
Amla, on the other hand, took full advantage of the life he got on 3, when he was dropped off a difficult chance by Rana, to first get to a superb half century in just 34 balls.
Punjab needed their captain Glenn Maxwell to step up the gas and the Australian wasted no time to settle down. He started off with two consecutive boundaries off medium pacer Jasprit Bumrah before smoking McClenaghan for two back to back sixes and then two fours to finish off the over.
Amla meted out special treatment to Sri Lankan pacer Lasith Malinga, dispatching him for two consecutive sixes twice in two overs to help himself reach the three-figure mark and the team to a mammoth score.
Source - Agency