It will be a virtual quarterfinal clash between the two sides at Kennington Oval but a lot will depend on the outcome of the Group A match between England and New Zealand in Cardiff to decide the equations.
If New Zealand win, Australia will have to beat Sri Lanka but if England triumph, they must beat the Islanders by a huge margin to surpass Black Caps' net run-rate, currently the best in the Group.
A win will seal Sri Lanka's place in the last four while a defeat will see them go home.
Sri Lanka's recent success against Australia will provide a psychological edge to them -- in the last 10 ODIs played between the two sides, Sri Lanka have won six while they drew the ODI series 2-2 earlier this year in Australia.
Australia have just one point from two games, starting their campaign with a defeat to England and then having their game against New Zealand washed out.
On the other hand, Sri Lanka were skittled out for a paltry 138 against New Zealand in their tournament-opener but a superb bowling show by slinger Lasith Malinga saw them very nearly defend the total before losing by one wicket.
Sri Lankan batsmen, however, gave a better account of themselves in their stunning run chase against England to romp home against the hosts. Led by Kumar Sangakkara's unbeaten 134, they chased down the 294-run victory target with relative ease to keep their semifinal hopes alive.