With an intense spotlight on his Test future, Labuschagne edged his fifth ball to slip off spinner Simon Harmer as Australia fell to 2-90 at lunch on day two of the third Test in reply to the Proteas' 329 at Newlands.
Australia had got off to a near-perfect start on Wednesday with Travis Head (41) and Matt Renshaw (27no) putting on 58 for the first wicket before a double blow.
Head attempted to cut the first ball of Harmer's spell from off stump and chopped on to his wicket, the fifth time he has been out in that fashion in eight innings.
That left all eyes on Labuschagne, who entered this Test well aware his future was on the line.
After cutting a tense figure earlier in the morning, he carried that approach into his innings and went back to a ball he should have gone forward to and edged it to slip.
Labuschagne will almost certainly have another chance to bat in this Test, but he appears a dead man walking.
If Australia had more batting depth on the tour or if this was a home series, he could well have been gone already.
Prior to this match, Labuschagne had scored between 30 and 49 in six of his past nine Test innings.
Australia's captain Pat Cummins put it bluntly last week when he declared those "aren't going to win too many matches" following the big second Test loss.
Labuschagne was the No.1 ranked batter in the world after his first 30 Tests, averaging above 60 and having chalked up 10 centuries in 52 innings.
In the 70 innings since, he has scored just one century and averaged 28.82. He has now gone 48 innings since his last century against England in the 2023 Ashes.
The Queenslander was briefly dropped in that time during a three-Test tour of West Indies, but Australia have for a long time had faith in him to lead the batting into the future.
Labuschagne had been in line to play in this Test at Newlands, even before Steve Smith's neck injury prompted Josh Inglis' late call up.
But it now appears almost certain he will be dropped for Australia's next Test against New Zealand, with Kurtis Patterson, Nathan McSweeney and Sam Konstas among the options to come in.
On Wednesday, former Test opener Simon Katich argued it was the right thing to do by Labuschagne to leave him out of the team.
"That is the pressure the selectors have put him under for an extended period of time," former Test player Katch said on SEN.
"They deserve to be in the same situation as him here.
"They put him in this situation by not making the decision to give him a breather and make the circuit-breaker decision.
"Everyone has been talking about it, they refused to do it. And I actually feel for him because I have been through it and it's not pleasant.
"It's a hard enough game when you're playing well, let alone when you have to think about everything technically and mentally and know you need a score."
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