If South Africa win Tuesday's Super Eights clash then they will be guaranteed the final last four spot and England will be out.
Pietersen, who was born in South Africa but switched allegiance after becoming frustrated at the lack of opportunities, has waged a war of words with Smith since returning to the country of his birth on tour in 2005.
Pietersen called Smith an "absolute muppet" for his on-field sledging during that tour.
"Graeme Smith and I do not get on but I must not be distracted," the 26-year-old Pietersen told the News of the World on Sunday.
"This is a massive game. It's a make-or-break game. If we win, we've a great chance of making the semi-finals. If we lose, we'll be flying out of the Caribbean on Sunday.
"Tuesday is do or die for England. It's not Kevin Pietersen v Graeme Smith.
"We won't be having a beer together afterwards. Neither of us have a problem with that. We will both be giving everything to come out on top - let's leave it at that."
Pietersen left South Africa in protest at the quota system which guarantees places in the international set-up for black players.
But he insists that the issue is history.
"The reality is that I am bored with the South Africa issue. It's old news. All my reasons for leaving have been well-documented," said Pietersen.
England coach Duncan Fletcher believes Pietersen will be able to handle the pressure of facing his own country.
"When he plays them, he is really motivated which is a positive for us," Fletcher said.
"South Africa motivate him just as much as Australia, probably more. I hope it drives him to put on one of those batting performances."
Pietersen, officially ranked the world number one batsman, hit three centuries on the 2005 tour of South Africa.
At the World Cup so far, he has 341 runs at an average of 56.83.