"This is the World Cup and it is a new tournament," Flintoff said.
"It's a massive game for us and, whatever happened in the winter, we will put to one side and we will just focus on Sunday. I've only played against them once in a one-day international so there is no history there."
Following their 82-run defeat by India in a day-night game on Wednesday, England face an anxious few days to find out if a second successive World Cup campaign is to end at the first-round stage.
Even victory over Australia, which would end a losing streak in one-day cricket spanning four years, may not be enough for England to stay in the competition because results from other matches will have a bearing on the group's final standings.
However, England arrived in Port Elizabeth on Thursday with victory over Australia as their chief objective and Flintoff, their leading performer against India, will go into the game in confident mood after his best all-round display in a one-dayer.
Flintoff took two for 15 from 10 miserly overs at Kingsmead and then smashed India's attack for three sixes as he top-scored for England with 64.
DECENT PERFORMANCE
"Irrespective of how I played, you are disappointed to lose," he said. "I may have put in a decent performance but it is the team that counts. If I'd gone for nought for 80 and got a duck, it wouldn't have mattered if England had won.
"I'm working on my game and trying to improve. Maybe it has taken longer than people thought, including myself, but I'm working hard and trying to get better."
Flintoff was sent home early from England's recent tour to Australia after failing to recover from hernia surgery and had to prove his fitness before being included in the World Cup squad.
He made his international return in the second match of the triangular series final against Australia in Melbourne, where England came within five runs of victory.
"I was very disappointed with the groin," Flintoff said. "I did my rehab but wasn't quite right when I went out there and had to go home and get fit for the World Cup.
"When I was at home, the specialist couldn't guarantee that I'd be alright for the World Cup. In December, when I sat down with him, he painted a pretty grim picture so I'm just very, very happy to be here.
"When I went home, I was still in some discomfort but, a week before I went away again, it improved."
