What happened next remains one of cricket's great mysteries, with the Queenslander's career now at a crossroads and the axe again hovering.
Labuschagne was not alone in disappointing on what was Australia's worst day of cricket this decade against South Africa on Wednesday.
But his outing was the most frustrating, as the tourists were all out for 99 and then 4-156 at stumps on day four after being asked to follow on, still trailing by 170 runs.
After being superbly caught in the first innings for 14, the 32-year-old acted like a man who knew his career was on the line during his second dig later in the day.
He nailed down, did the hard work, was as relieved as anyone when he overturned an lbw review by 4.7 millimetres on review and again got his way into the 30s.
Then he tried to take on spinner Simon Harmer into a howling wind and was caught at a deep mid-on for 39.
When Labuschagne hit the 10th career century against West Indies at Adelaide Oval in December 2022, they had come in his first 51 innings as a Test player.
In the 69 innings since, he has hit just one, with that coming against England in the 2023 Ashes some 26 Tests ago.
His average since December 2022 is less than half what it was, now 29.29 across that time.
Australia have made no secret of the fact Labuschagne needs a big score, but tellingly six of his last nine scores have now been between 30 and 49.
"He did a lot of hard work once again," Australia coach Andrew McDonald said.
"It feels like I'm on repeat around the number of 30s that he has got. You would say that's a danger period for him.
"But when you do that hard work, you've got to cash in and unfortunately that wasn't the case for Marn.
"He'd be disappointed, we're disappointed and we find ourselves in this situation."
Whether Labuschagne survives the axe to play in Cape Town next week remains to be seen. He was dropped last year for the three-match West Indies series, but returned three Tests later.
Nic Maddinson appears almost certain to go, while Beau Webster's returns are also below par.
Cameron Green and Josh Inglis are fit again, while Cooper Connolly and Sam Harper are also on tour.
The fallout from Wednesday will be vast, but Australia must pick a side to win in Cape Town and take victory in the series.
McDonald would not discuss that situation midway through a Test, adamant he didn't want to "hang players out to dry".
But big conversations and decisions do loom for the coach and fellow selectors in coming days.
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