Australia are facing a lengthy and thorough fall-out from the latest Cape Town disaster, after they were bowled out for 111 in pursuit of 288 for series victory on Saturday.
Billed as one of the biggest days of Test cricket in years with the series level, Cummins admitted after Saturday's 176-run capitulation that it was effectively done from the end of the first over.
Matt Renshaw and Marnus Labuschagne were both dismissed in Kagiso Rabada's opening six balls, starting the rot.
Spinner Simon Harmer then ripped the heart out of Australia with 6-16, ending the match just before tea when he bowled Josh Hazlewood.
In all four Australians scored ducks, while Travis Head (14) and Cameron Green (27) were the only recognised batters to reach double figures as the tourists fell to 8-62.
The chaos was summed up when Green at one point defended a ball past Marques Ackerman at silly point, took off and ran Josh Inglis out in the process.
All that came just a little over a week after Australia threw away a near-unbeatable position in the series when bowled out for 99 in the second Test in Gqeberha.
Asked if change was required as a result, Cummins conceded: "We've lost two games in a row. It's fair to be asking those questions.
"We'll be asking them internally as well.
"We are a very good side. But I think we need to get a little better if we want to get back to No.1 and where we can be.
"Maybe that's a change of style. Maybe it's a change of personnel in some instances. Give us a couple of weeks on that."
Labuschagne is almost certain to go, with his horror tour ending in the first over of Friday when he was lbw trying to leave Rabada (3-39).
But he was far from alone on Saturday, with Newlands again proving a graveyard for Australian cricket as it has on several recent tours.
Rabada also had Renshaw caught down legside in the first over, before a driving Travis Head edged him to gully shortly after.
Alex Carey was reverse-sweeping Harmer straight to backward point, before Cooper Connolly edged behind in the same over.
Ultimately, only a late 90-ball vigil from Cummins and unbeaten 33 from Nathan Lyon saw Australia avoid being all out for less than 100 in consecutive Tests for the first time since 1936-37.
"There were a few really poor decisions," Cummins said.
"I know it was a day-five wicket, but I don't think it was drastic. There's runs to be scored out there, there's lots of balls to face.
"We've got to get better. It's happened a few times. When we turned up here today, we thought that chase was very achievable."
The result leaves Australia with losses in three of their past five Tests, with the shock defeat to Bangladesh in Darwin no longer a one-off.
But Cummins insisted all was not broken with the side, ahead of a home series against New Zealand and marquee tours of India and England.
"Ideally we would have had a little bit better record than that," he said.
"I still think we're a really good side ... We had our moments in every Test, a couple of Tests ago we had a big win against them.
"We're really well placed, but clearly there's been a few moments in the last couple of Tests where a few more of us need to step up."
Australia will be left to rue several moments in a series where a draw looked the worst possible outcome, like when they had South Africa 6-110 on day three of a wet second Test.
But the Proteas fought back, rolled through Australia and won to level the series.
Australia then claimed a 100-run first innings lead in Cape Town and had South Africa 4-140 in the third innings, before Ryan Rickelton and Wiaan Mulder's centuries on day four.
Ultimately, that was enough for the Proteas take first spot off Australia in the ICC Test rankings, while also leapfrogging them into the top-two in the race to next year's World Test Championship final.
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