Just as Australia's Beth Mooney had done for the champions to oust Pakistan the day earlier, de Klerk came up with one of the World Cup's great innings on Thursday, hammering a scintillating unbeaten 84 off 54 balls as the Proteas stunned the powerful hosts by three wickets.
De Klerk plundered five sixes and eight fours, enjoying some crucial lower-order stands, and joyously hit two of her last three balls from Amanjot Kaur for maximums to seal the win with seven balls remaining.
Earlier, captain Laura Wolvaardt had led the way with 70 off 111 balls as South Africa, having been set a target of 251, made it to 7-252 with seven balls remaining.
It was a truly special knock from the 25-year-old de Klerk, who admitted she was "lost for words" after she'd even eclipsed another astonishing innings from India's Richa Ghosh, who'd dragged the hosts from a precarious 6-102 with her thunderous 94 off 77 balls.
De Klerk's match-winning knock was so good that Wolvaardt was also left dumbstruck afterwards, sighing: "It was incredible. I don't think I have seen something like that all my career, that was a special innings. I am still at a loss for words."
De Klerk had also taken 2-52 with the ball, while her fellow allrounder Chloe Tyron also made a huge contribution, picking up 3-32 to go with a vital 49 off 66 balls.
India had been fancied to overhaul the still unbeaten Aussies, who had one match wiped out by rain last weekend, but Alyssa Healy's side now remain top on five points, one ahead of England, India and South Africa, the four teams who look most likely to qualify as semi-finalists.
England, who've played a game less, can go top by beating Sri Lanka on Saturday while Australia's next match against India takes on an even more significant feel at Visakhapatnam on Sunday with Harmanpreet Kaur's side perhaps starting to feel the pressure should they lose a second match in a row.
"We have done lots of good things and to finish off the game, take the game deep and get over the line is great," said de Klerk.
"I do like being under pressure. I love the World Cups, and there's no bigger stage than playing at India at their home. We had to be at our best, and it is great to get over the line.
"We are capable of beating the best sides in the world, but we just had to take it deep. We are a very good side in the back-end. Chloe took the pressure off me, also Laura was great and that power-hitting comes quite natural to me.
"That's my role in the side. I have to finish off the game. I had some time, it looked a good wicket and I wanted to give myself some chance."
South Africa will play Bangladesh next on Monday, but the Australians won't meet the Proteas until the last round of group matches in a fortnight's time at Indore.
