ICC World Cup 2019: Usman Khwaja explains Australia's revival and recent form
Steve Smith dropped down the order and was not required as Australia chased down Sri Lanka's 239 with 31 balls remaining for the loss of five wickets.
Sri Lanka batted first, with only two players - opener Lahiru Thirimanne (56) and Dhananjaya De Silva (43) - scoring more than 30 as they reached 239 for eight from their 50 overs.
Despite the early dismissal of Aaron Finch, fellow opener Usman Khawaja came back from an early injury scare after he was hit on the knee while fielding to top-score with 89 from 105 balls and put Australia ahead of the required run-rate.
Useful contributions from Glenn Maxwell (36), Shaun Marsh (34) and Marcus Stoinis (32) helped see their side over the line.