Sri Lanka's Angelo Mathews said he is hoping his side can continue to pile on the runs, despite having to make changes for their Cricket World Cup clash with Australia.

The sub-continent side have won three straight games since a tournament-opening loss to New Zealand, but have lost Dimuth Karunaratne (fractured finger) for the campaign - while spinner Rangana Herath (finger) is sidelined for their date with the co-hosts in Sydney on Sunday.

Mathews said Seekkuge Prasanna, who has 21 wickets in 22 ODIs, should fill the void for Herath if selected.

"He has a good chance, because out of the eight batters, they have about seven right-handers so he comes into play," Matthews said of leg-spinner Prasanna.

He added: "We don't look to change our composition too much. 

"We are forced to make a couple of changes because Rangana and Dimuth is out of the team. 

"But it has worked for us so far, so we don't want to change a lot of things. 

"But I think whoever comes in, the batters are doing pretty well so hopefully they will continue in the same matter."

Mathews also hinted Upul Tharanga was the likely replacement for Karunaratne, the 176-ODI veteran to earn a reprieve having played just five 50-over matches since July 2013.

Regardless, Mathews said he backed his side to out-bat any opponent.

"Three hundred is a gettable score on good wickets, but more often than not, we should be able to limit most oppositions to under 300. So hopefully we can do that tomorrow if we bowl first," he said.

On their poor record against Australia at World Cups - they have lost all five times against them - Mathews said history was selective.

"I don't think so," Mathews said, when asked if beating Australia at a World Cup was a mental barrier. 

"Recently when we clashed against the Australians, we've beaten them in England, and in Australia a few years ago. We have the capacity, but they're a very hard team to beat."