Choosing to bat in Ahmedabad on Sunday in a rematch of the 2024 World Cup final, South Africa surged to a commanding 7-187 following a remarkable recovery from a precarious 3-20.
In reply, India's timid top-order faltered swiftly, and their innings never quite escaped the grip of scoreboard pressure. They were bundled out for 111 in 18.5 overs, slipping to their first defeat of the World Cup.
David Miller's breezy 63 earned him the player-of-the-match award for the Proteas.
Earlier, India had quickly taken the sting out of South Africa's top-order following Aiden Markram's decision to bat first at the Narendra Modi Stadium.
Jasprit Bumrah bowled Quinton de Kock, while Arshdeep Singh had Markram snared at mid-off to leave South Africa without any of their openers inside three overs.
Bumrah's control (3-15) shone again when, with a deft change of pace, he deceived Ryan Rickelton, who chipped tamely to Shivam Dube at mid-off.
From there, a blistering 97-run partnership between Miller and Dewald Brevis (45) not only halted the slide but also turned the heat back on India.
Brevis missed a well-deserved half-century but Miller powered to his in just 26 balls.
Spinner Varun Chakravarthy removed Miller in the 16th over, but Tristan Stubbs provided the last flourish with an unbeaten 44 off 24 balls that included three sixes.
India's chase began in near-identical fashion to South Africa's innings, but without the same rescue act.
With three left-handers in India's top three, off-spinner Markram began with the new ball and the ploy soon paid off.
Markram dismissed the in-form Ishan Kishan in the first over and Marco Jansen dismissed Tilak Varma in the second.
Opener Abhishek Sharma (15) avoided a fourth successive duck but neither he nor Washington Sundar (11) could provide the stability that India needed.
India captain Suryakumar Yadav (18) departed in the 10th over, leaving India reeling at 5-51.
Keshav Maharaj then effectively extinguished India's fading hopes in one telling burst.
The left-arm spinner dismissed Hardik Pandya (18), Rinku Singh and Arshdeep Singh in an eventful 15th over.
Shivam Dube's gallant 42 at least provided some respectability to India's margin of defeat, but Marco Jansen dismissed him and Bumrah with successive deliveries to finish with 4-22.
