Sri Lankan fast bowler Kasun Rajitha took three wickets in successive overs to increase South Africa's woes on the first day of the second Test on Thursday.
South Africa were 185 for seven at tea, with Quinton de Kock, their last recognised batsman, on 68 not out at St George's Park.
It could have been worse for South Africa, who need a win to salvage a share of the series after a surprise defeat in the first Test in Durban. Both not-out batsmen, De Kock and Kagiso Rabada, survived catching chances shortly before tea.
South Africa made a poor start after winning the toss. They lost three wickets with the total on 15, two of them to successive balls from Vishwa Fernando, and were 73 for four when captain Faf du Plessis was bowled by his opposite number, part-time bowler Dimuth Karunaratne, with the last ball before the interval.
The hosts seemed to be recovering when Aiden Markram and Quinton de Kock put on 57 at almost a run a ball for the fifth wicket before Markram was leg before wicket to Rajitha for 60.
Rajitha followed up with the wickets of new cap Wiaan Mulder for nine and Keshav Maharaj for nought.
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The left-handed De Kock went to his third half-century of the series off 51 balls but was dropped on 55 when Dhananjaya de Silva could not hold a high chance at gully off Rajitha.
Rabada, on eight, hammered back a return chance to left-arm spinner Lasith Embuldeniya in the last over before tea. Embuldeniya left the field with an injured left thumb and could not complete the over.