Pietersen hammered 97 off 84 balls as England gained a six-wicket win over the South African second string in their only limited overs warm-up game ahead of a seven-match one-day international series, starting in Johannesburg Sunday.
The tall, powerful Pietersen, 24, was educated in South Africa and played against the 1999/2000 English tourists in his debut match for KwaZulu-Natal, batting at number nine and hitting an aggressive 61 not out. He had been picked mainly as an off-spin bowler and took four wickets.
He took advantage of a British passport and qualified for England by playing county cricket for Nottinghamshire, with his batting soon outstripping his bowling. He made his international debut in the one-day series against Zimbabwe last November.
Not originally picked for the South Africa leg of the tour, he was added to the current squad following impressive performances in Zimbabwe.
"It was a late Christmas present for me," said Pietersen of his call-up.
"I'm just delighted to be here contributing to a good England team. Hopefully I can take this form into Sunday's game if selected."
Pietersen and Ian Bell, 22, who also made his one-day international debut in Zimbabwe, put on 169 off 164 balls for the fourth wicket after England made a shaky start in pursuit of a South Africa A total of 251 for eight on an easy-paced pitch.
Pietersen reached 50 off 63 balls then raced to 97 off only 21 more deliveries before falling to a diving catch at midwicket when he played a forcing shot against medium-paced Adam Bacher. His innings included nine fours and three sixes.
Bell made an unbeaten 87 off 104 balls with eight fours.
Opening batsman Morne van Wyk made 104 for South Africa A. He and captain Boeta Dippenaar (66) put on 108 off 140 balls for the second wicket but the remaining batsmen were unable to capitalise on the good start.
England fielded all the one-day specialists who joined the side for the limited overs series and their side included only two players, Marcus Trescothick and Geraint Jones, who played in the final Test earlier in the week when England completed a 2-1 series win.
South Africa A