Buttler clubbed six fours and four sixes in his 43-ball knock of 71 as England raced to the fourth highest ODI total in Perth after being sent in to bat by stand-in Australian captain George Bailey.
Ben Stokes (70 off 84 balls) and Ian Bell (55 off 52) also made important half-centuries as the tourists look to a avoid a record-equalling 10th straight defeat to Australia across all formats.
Buttler and the in-form Eoin Morgan (33 off 33) combined for a sixth-wicket stand of 71 from just 51 balls after England had managed only 24 runs from the batting powerplay during overs 36-40.
James Faulkner (4-67) was the pick of the bowlers for the home side, while spinner Glenn Maxwell (1-37) was economical during the middle overs.
New Zealand (2007) and Zimbabwe (2001) previously posted second-innings ODI totals over 300 in Perth, but both were unsuccessful run chases.
Australia has also rested batting stars Michael Clarke, David Warner, Shane Watson and Brad Haddin from this match.
Bell and Alistair Cook (44) powered England to 87 from just 12 overs before the England captain was bowled by the spin of Maxwell.
Shaun Marsh put down two tough chances at first slip when Bell was on 52 and Stokes on 29 as the England pair produced another half-century stand.
But Bell was caught at short fine leg by Faulkner just three runs later as he attempted to flick Dan Christian down the leg side.
England persisted with Stokes at No.3 despite his failure in the last match Sydney and he failed to disappoint with his maiden ODI half-century.
Gary Ballance was fortunate to survive a run-out chance on 11, but struggled to make an impact before he skied a catch to Steve Smith at cover.
England appeared unlikely to move past 300 when Stokes and Ravi Bopara (three) were dismissed during the batting powerplay, before Buttler unleashed on a wayward Australian attack.
Allan Border medallist Mitchell Johnson (0-72), James Pattinson (1-63) and Nathan Coulter-Nile (1-62) were all punished by an unrelenting Buttler as England scored 93 runs from the final 10 overs.
Faulkner found himself on a hat-trick in the final over after dismissing Buttler and Tim Bresnan in consecutive deliveries, but Stuart Broad cracked the decisive last ball through cover for a boundary.
England has lost its past nine matches combined in all formats and defeat on Friday would equal the mark set twice before in 1993 and 2001.
Australia regained the world No.1 ranking in one-day cricket on Wednesday when New Zealand defeated India, but need to win to retain top spot.