The opening batsman's innings was the centrepiece of England's 195 for five at Chester-le-Street as they looked to level the two-match series at 1-1 after a 39-run loss at Southampton on Thursday.
Pakistan-born leg-spinner Fawad Ahmed, wicketless on debut at Southampton, took his first international wickets, including two in the last over, to finish with three for 25.
Hales, who made 99 in a T20 international against the West Indies at his Nottinghamshire home ground of Trent Bridge last year, shared an opening stand of 111 with Michael Lumb (43).
England, in a mirror image of Thursday's 39-run defeat in the first T20 at Southampton, were sent into bat by Australia captain George Bailey on Saturday.
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The powerplay ended with England 61 without loss off six overs after a blizzard of boundaries.
Hales drove a straight six as James Faulkner's opening over went for 19 runs and left-hander Lumb struck all-rounder Shane Watson high over long-on for six.
However, the first wicket partnership was broken when Lumb top-edged a sweep off Ahmed and was caught behind by wicketkeeper Matthew Wade.
England, though, were still well-placed at 111 for one in the 12th over.
Luke Wright added a quickfire 30 before he was well caught by a leaping Mitchell Johnson at mid-off after driving a Faulkner full-toss.
Hales, off the last ball of the penultimate over, was caught by David Warner, running in from long-on, off Faulkner to end a 61-ball innings featuring 11 fours and two sixes.