Sri Lanka's Pathum Nissanka on Monday said the team will learn from their mistakes after going down to Australia in the World Cup and strive to win the remaining matches.

A five-wicket loss at Lucknow's Ekana Stadium made Sri Lanka slip to their third successive defeat in the round-robin tournament where each team will play nine league matches.

Nissanka and fellow opener Kusal Perera put on 125 runs before the batting, which posted totals of over 325 in the previous matches, imploded to 209 all out in 43.3 overs.

"That's the nature of cricket. We performed admirably in the previous two games, but such fluctuations can occur," Nissanka told reporters.

"Our focus now is to learn from our mistakes and strive for strong performances in the upcoming matches."

Nissanka made 61 and the left-handed Perera hit 78 before both the batsmen fell to Australian captain Pat Cummins and legspinner Adam Zampa soon had the opposition on its knees with figures of 4-47.

Five-time winners Australia reached their target of 210 with 14.4 overs to spare and Nissanka said it's all to play for in the race to the semifinals.

"Our mental level is good," said Nissanka. "We hope to play well and win the remaining matches."

Cummins and left-arm quick Mitchell Starc took two wickets each while Glenn Maxwell wrapped up the Sri Lanka innings with his off spin.

"To be candid, the opposition's bowlers consistently hit good areas during the middle overs, which created a challenging situation for our batsmen," said Nissanka.

"Unfortunately, we couldn't handle it as effectively as we would have liked. Had we managed to play better, we could have achieved a total of three hundred runs."

Sri Lanka's left-arm pacer Dislhan Madushanka raised hopes of a fightback with the early wickets of David Warner, for 11 and Steve Smith, for a duck.

But Mitchell Marsh hit 52 and wicketkeeper-batsman Josh Inglis made 58 to put Australia on course before Maxwell, with his 21-ball 31, took them home.

Nissanka said batting became better under lights but Sri Lanka did not have a total to defend.

"To be frank, the pitch appeared to ease up somewhat once the lights came on. This played into their favour, enabling them to bat with their usual flow and a positive approach," he said.

"Our bowlers, on the other hand, struggled to maintain lengths. If we had performed better, we could have set the stage for a competitive match."

Sri Lanka next play the Netherlands on Saturday at the same venue and effectively need to win their remaining six games to keep the chances of making the final four in their own hands.