Hales blasted 84 runs from 51 balls and Buttler 68 from 32 deliveries in a dominant display of power hitting.
Australian captain Aaron Finch (35) earlier won the toss and chose to bowl, making five changes to the side that beat the West Indies last week.
Among the changes was the decision to rest pace trio Pat Cummins, Mitchell Starc and Josh Hazlewood as well as leg spinner Adam Zampa.
Their replacements failed to come to terms with the powerful stroke play of the England opening pair, who hit 20 fours and seven sixes between them.
Buttler, back in the side after a two-month injury lay-off, showed no signs of rust as he blasted 16 runs off the first over, hitting Cameron Green for four boundaries.
He and Hales smashed 50 off the first five overs and brought up the 100 in just the ninth over.
Nathan Ellis (3-20) was the pick of the bowlers and finally made the breakthrough when Buttler attempted to hit down the ground, only to miscue to mid-off, where Kane Richardson took a comfortable catch.
Ben Stokes came and went for nine before Hales was caught in the deep off Richardson to leave England 167-3 midway through the 16th over.
Although they lost wickets at regular intervals, the English pushed past 200 to set the Australians a challenging total.
