With England already progressing to the semifinals from Group A, any of the remaining three teams - Australia, Sri Lanka and New Zealand - can join the English in the last four, with the final match of the group -- between Australia and Sri Lanka at The Oval - set to be the deciding factor.
New Zealand currently have three points with a good nett run rate, while Sri Lanka are on two points and Australia on one.
A win for Australia on Monday evening will see New Zealand tied with the Aussies on three points each with the nett run rate then coming into play - Australia will need to post a big win to catch up with the Kiwis' run rate.
If Sri Lanka win, it becomes easy with the Island side moving to the semifinals along with England.
"The mood in the camp is very good," Sri Lanka skipper Angelo Mathews said. "We're feeling very confident, but I think tomorrow (Monday) it's a fresh game. We must start from zero once again.
"So we need to be up for the game against Australia because we all know that Aussies play well. They've not been in the best of form, but still, we can't be complacent against them because they've got some really good players, so we have to be on our guard all the time."
Australia have had a torrid time of it off late, both on and off the pitch, but the side could be boosted by the return of captain Michael Clarke, who missed the first two matches due to a back injury.
"I don't know at this stage," Clarke said when asked if he would be fit for the game against Sri Lanka. "I'll have to train today (Sunday) with the boys and see how I pull up tomorrow.
"But I'm hopeful, there's no doubt about that. But yeah, I really need to wait and see how I pull up tomorrow morning after training again today."
Clarke remains confident of pulling off a win against the Lankans come Monday.
"I think every game you play in this tournament you know you've got to play your best to have success, so our focus over the past three days has been about making sure we get ready to walk out there tomorrow and be able to execute our skills as well as we can," he said.
"I thought obviously the rain played a part yesterday (Saturday), but a lot of the guys came and trained indoors. The day before, we trained really well as a team, and hopefully we get outside this afternoon and finish our preparation. But I know all the guys are looking forward to playing against Sri Lanka tomorrow."
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Expected lineups: Australia: Watson, Wade, Hughes, Bailey, Voges, Marsh, Maxwell, Faulkner, Johnson, McKay, Doherty.
Sri Lanka: Dilshan, Perera, Sangakkara, Jayawardene, Chandimal, Thirimanne, Mathews, Kulasekara, Perera, Herath, Malinga.