Dawid Malan smashed a brilliant 99 not out to take England to the top of the world rankings with a comprehensive nine-wicket win over South Africa in Cape Town.
Chasing 192 to win and seal a 3-0 series sweep, Malan (99no from 47 balls) and Buttler (67no from 46) were in imperious form as they put on a world second-wicket partnership of 167 and wrapped up the victory for England in just 17.4 overs.
South Africa had appeared very well placed at the halfway stage after a blistering and unbroken 127-run stand between Rassie van der Dussen (74no from 32) and Faf du Plessis (52no from 37) had lifted them to 191-3 after a shaky start.
Malan and Buttler saw things differently though and England can celebrate leapfrogging Australia to reach No 1 in the ICC's T20I standings before focus turns to the first one-day international on Friday.
There was also a moment to savour for Chris Jordan during the South Africa innings as he overtook Stuart Broad to become England's record wicket-taker in T20 cricket when he dismissed Quinton de Kock.
Having won the toss and opting to bat, South Africa started well as Temba Bavuma smashed Sam Curran over square leg for six and Quinton de Kock got after Jofra Archer, hitting another maximum over fine leg.
However, they suffered a setback when De Kock fell to Jordan (1-42) in the fifth over, miscuing the ball to Tom Curran at mid-off, to give the England seamer his record-breaking 66th T20I wicket.
Bavuma progressed to 32 before tamely chipping the last ball of Ben Stokes' first over to Jordan at mid-off and when the England all-rounder had Reeza Hendricks (13) caught behind off a slower ball in his next over, South Africa were struggling at 64-3 in the 10th over.
Du Plessis and Van Der Dussen's partnership began steadily as they negotiated the end of Adil Rashid's (0-20) economical spell but the latter's brutal six over square leg off Stokes (2-26) had already provided a glimpse of what was to come.
For all that England's bowlers will be disappointed with their execution in a final five overs that cost 84, Du Plessis and, in particular, Van Der Dussen were merciless in punishing the slightest error as they repeatedly sent the ball over the ropes.
Du Plessis nailed Tom Curran for two sixes in an over before Van Der Dussen got stuck into Archer in the next, taking him for 22 including two fours and two sixes to reach a 23-ball fifty.
Three fours in a row off Sam Curran took Du Plessis to his half-century, from 37 balls, before Van Der Dussen nailed a couple more maximums in the final over from Jordan.
England lost the out-of-form Jason Roy (16), lbw to Anrich Nortje (1-37), in the fourth over but quickly got over that disappointment as Malan raced to 14 off three with back-to-back fours off the Proteas paceman and a six off Lutho Sipamla, the seamer brought in for the injured Kagiso Rabada.
While Malan was in supreme touch from the off, Buttler was going at less than a run a ball at the halfway stage of the chase. That all changed in the 11th over as the England opener launched Sipamla's first two balls over the legside for six and added a boundary through the offside four balls later.
That signalled the start of an England onslaught as 19 came off the next over from Tabraiz Shamsi (0-57), a six apiece for Buttler and Malan, who also played a glorious shot over extra cover for four to bring up his 10th T20I fifty in just in 19th innings, from 26 balls.
Shamsi's next proved even more costly, Buttler starting it with six over cow corner and Malan ending it with a mighty blow over deep midwicket.
England suddenly needed less than a run a ball and with a century in sight, Malan belted Sipamla (0-45) over long on to move to 94 and four more took him to within two of a second T20I hundred.
However, a wide in between meant just one more was required and a single to win the game left him agonisingly short of the milestone.
Watch the first one-day international between South Africa and England on Sky Sports Cricket from 10.30am on Friday.