Electing to bat, India lost opener Smriti Mandhana (8) cheaply with just eight runs on the board.
But the other opener, Kamini, in the able company of Poonam put on an unbroken 203-run partnership together for the second wicket on day one to take the team past 200-run mark.
While Kamini's unbeaten 100 came off 305 balls, studded with 13 fours, Poonam remained not out on 100 off 297 deliveries with the help of same number of boundaries as her partner.
The two girls batted brilliantly throughout the day, even as the South Africans bowlers tried in vain to get at least one of them out.
The hosts batted for a total of 102 overs, losing just one wicket.
The only bowler, who finished with a scalp, was Chloe Tryon, who ended with one for 23.
Brief scores:
India Women 1st innings: 211 for one in 102 overs (Thirush Kamini 100 not out, Poonam Raut 100 not out; Chloe Tryon 1/23).
Image: Thirush Kamini
Photograph: Ben Hoskins/Getty Images