Leg-spinner Adam Zampa took four wickets as Australia bowled out Sri Lanka for 209 despite an opening century stand by the island nation in a World Cup match that will give one of the teams a first win.
Pathum Nissanka (61) and Kusal Perera (78) put on 125 runs for the first wicket before Australia hit back to end the innings in 43.3 overs at the Ekana Stadium in Lucknow.
Skipper Pat Cummins took down the openers to trigger a collapse and Zampa joined forces to return figures of 4-47.
Sri Lanka elected to bat first and the right-left batting pair of Nissanka and Perera took on the opposition bowlers with regular boundaries -- 20 between them.
Perera reached his fifty with a boundary off Marcus Stoinis amid applause from the dressing room and a few Sri Lankan fans at a largely empty 50,000-seater stadium.
Nissanka soon got his second successive half-century as Sri Lanka charged ahead.
Cummins got Nissanka through a good outfield catch by David Warner and then bowled Perera.
Zampa sent back skipper Kusal Mendis and Sadeera Samarawickrama on consecutive balls between overs to be on hat-trick avoided by Dhananjaya de Silva.
Rain interrupted play for about 25 minutes and the break only gave Australia more power to return with wickets as left-arm quick Mitchell Starc bowled De Silva.
Sri Lanka kept losing wickets and a direct throw by Cummins ran out Dunith Wellalage for two.
Zampa kept up his attack and got two more wickets including Chamika Karunaratne, who was only called up to replace injured captain Dasun Shanaka at the weekend.
Charith Aslanka made 25 before being bowled by Glenn Maxwell as the Sri Lankan innings ended.
Sri Lanka named two changes to their team, which has scored over 325 runs in each of their two losses.
Five-time winners Australia have also lost their first two matches after they went down to India by six wickets and then suffered a 134-run thrashing against South Africa.
Brief Scores: Sri Lanka 209 all out in 43.3 overs (K. Perera 78, P. Nissanka 61; A. Zampa 4-47) v Australia