Leg spinner Adam Zampa took four wickets as Australia bowled out Sri Lanka for 209 despite an opening century partnership by the island nation, giving one of the teams their first win in a World Cup match.
Pathum Nissanka (61) and Kusal Perera (78) made a 125-run partnership for the first wicket at the Ekana Stadium in Lucknow, after which Australia counter-attacked and ended the innings in 43.3 overs.
Captain Pat Cummins demolished the team by dismissing the openers and Zampa returned with figures of 4-47.
Sri Lanka chose to bat first and the right-handed batting pair of Nissanka and Perera faced the opposition bowlers with regular boundaries – 20 between them.
Perera completed his half-century by hitting a four off Marcus Stoinis amid applause from the dressing room and some Sri Lankan fans in an empty stadium with a capacity of 50,000 spectators.
Nissanka soon scored his second consecutive half-century and Sri Lanka went ahead.
Cummins dismissed Nissanka with a good catch in the outfield by David Warner and then bowled Perera.
Zampa sent back captain Kusal Mendis and Sadira Samarawickrama with consecutive balls between the overs, but Dhananjaya de Silva did not take a hat-trick.