Both teams have a chance to top the group and face a relatively weaker team from Group B in their quarter-finals, with Pakistan on eight points from five matches and Australia nine from five.
Depending on the finishing positions, Pakistan could even end up facing arch-rivals India in Ahmedabad in the quarter-finals.
But Afridi refused to be drawn in the possible permutations, saying he has a definite plan to beat Australia who are on an unbeaten 34-match World Cup streak stretching back to 1999.
"We have made some plans against them because they are very strong mentally and physically, so you will see in the game we will do something new against these guys," said Afridi on Friday.
"We know that this game is very important for us to end in a good position in the group. If we win, we will go into quarters with a win and a good, positive attitude, which is more important," said Afridi.
Pakistan were the last team to beat Australia in a World Cup match, their 10-run win coming in the 1999 tournament at Leeds.
Afridi admitted Australia was a strong team.
"They are very professional, they are a good batting and bowling side as well. They know how to bowl reverse swing, especially when Brett Lee comes back and Shaun Tait as well.
"They know how to use these condition as well. But we know our strengths too, we know how to tackle and deal with these guys so we are well-prepared," added Afridi, the leading wicket-taker in the tournament with 16.
Afridi hinted Pakistan might bring in Umar Akmal, who has recovered from a finger injury which forced him to miss the team's last match against Zimbabwe, in place of misfiring opener Ahmed Shahzad.
Shahzad has managed just 51 runs in five innings.
"We have a settled combination, but we can make one change. Umar is available for selection as he has recovered from injury," said Afridi, who would not be drawn on whether retiring paceman Shoaib Akhtar would play.
Akhtar on Thursday announced he will retire from international cricket after the World Cup.
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