David Warner's first act as captain of Australia was to call incorrectly at the toss in Dambulla, where Angelo Mathews chose to bat.
It meant that for the third consecutive time from three games in this series, Australia would have to chase down a target.
Sri Lanka made no changes to their side in what will be Tillakaratne Dilshan's final ODI before retirement.
Australia, though, made three changes, the most notable being the result of captain Steven Smith flying home mid-series to rest up ahead of a busy upcoming period.
Shaun Marsh came in for his first game of the series in place of Smith, with Usman Khawaja once again missing out.
The Australians also dropped allrounder Moises Henriques and spinner Nathan Lyon, a surprising move given that the Dambulla pitch appeared to be dry and was expected to take plenty of turn.
Sri Lanka only managed to obtain 226 in 49.2 Overs. Dinesh Chandimal contributed with 102 runs while Thilakaratne Dilshan scored 42 runs, setting a target of 227 runs for the Kangaroos to chase.
Tillakaratne Dilshan's final ODI inings