South Africa knew 621 was a mirage.

Their score at SuperSport Park, built on former captain Faf du Plessis' 199, seemed too good to be true ... because it was. A depleted Sri Lanka were down to one frontline bowler for parts of that innings and, although it still took application to get runs on the board, the challenge of scoring them was greatly reduced.

But does that mean 84 for 9 is reality?

Bearing in mind the context (the collapse came after South Africa had reached 218 for 1, 61 runs ahead with oodles of batting to come) and the circumstances (the Wanderers surface quickened up on day two and the ball was moving around substantially) and you might be tempted to call it an aberration. But look at recent history, and you will have to question whether this showing at the Wanderers simply reflects the true state of South Africa's batting.

Last season, South Africa lost five wickets for less than 100 runs at some point in all 14 Test innings against India and England, and five for less than 50 runs in seven of those. Wickets fell in clumps at every stage of their innings, bookended by the tail folding in Vizag and the top and middle order stumbling at the Wanderers. And there are no mitigating circumstances, such as unplayable surfaces, to justify their performances. The pitches in India were good enough for the hosts to register seven centuries in the series between them, while at home, England scored three hundreds to South Africa's zero.

Lack of confidence appears to be South Africa's biggest issue at present, with a few players in need of technical tweaks, and it's something that can only be fixed with form. The domestic competition provides a place for players to re-find their feet, as it did for Aiden Markram and Dean Elgar who both scored first-class centuries (Markam has three) in the lead-up to this series.

It's not surprising then, that in such a run-desert, Elgar has been the oasis. Since January 2019, Elgar has scored more runs than all the other openers combined and is second only to Quinton de Kock among the rest of the line-up. Take de Kock, Elgar and Faf du Plessis away and no South African batsmen has scored more than 367 Test runs in the last two years, which suggests that the newcomers are not making the step up as well as it was hoped they might.

Markram has just made his return from injury (although there had been pressure mounting on him before he broke his hand and then his finger) so we'll cut him some slack and put the the spotlight on Rassie van der Dussen and Temba Bavuma, who are both being spoken about as candidates for the Test captaincy and have to start converting.

Van der Dussen is newer on the international scene and has done better so far, especially in this Test with a knock that started patiently and built promisingly. After waiting 25 balls for his first run yesterday afternoon, he showed his strength on the pull and the drive this morning and though he was dropped on 44, once he got his half-century, it didn't seem there was too much in the way of him carrying on. Then, he was strangled down the leg-side, attempting one swipe too many. Van der Dussen has now gone 43 international innings across all formats without a century, even though he appears to have the temperament to score many.

Bavuma's drought is much longer - five years almost to the day - since his only Test century and the concern around him now is the ways he has been getting out. After walking at SuperSport Park, he shouldered arms to an in-ducker when he should have offered a shot. By the time Bavuma was dismissed, Sri Lanka were already well into the tail so perhaps there's little more he could have done, but a handy not-out would have done his average some good and showed a level of responsibility.

Credit must go to Sri Lanka's attack for showing glimpses of what could have been had more of their first-choice players been available to them through this series. Vishwa Fernando, who was the leading wicket-taker when Sri Lanka beat South Africa two years ago built on that with his maiden five-for and has now taken more wickets than any other Sri Lankan seamer in South Africa.

Vishwa found seam movement and, for the most part, pitched it up and lured the South African batsmen in the channel outside off. De Kock and Nortje both nicked off that way. Equally impressive was debutant Asitha Fernando, who made good use of the bounce with back-of-a-length deliveries - one so short it sconed Lungi Ngidi - and deserved at least one more wicket. Van der Dussen was dropped off Asitha's bowling.

But Sri Lanka's find of the tour must be Dasun Shanaka, who last played a Test three years before this series, and was expected to be a bit-part bowler in this series. Instead, he stood up in an injury crisis at Supersport Park, and snagged van der Dussen and du Plessis to open South Africa up here. His set-up of du Plessis, with a lifter on the penultimate ball of his 12th over and a fuller one with the final ball, to have him caught behind for 8, was when the momentum of the innings switched camps. Van der Dussen had fallen four overs before, de Kock went the over after, and Sri Lanka had South Africa by the neck. They went on to force a choke, but it has probably come too late.

Dimuth Karunaratne has pushed them into a lead but, with three days left in the match, it will need to swell closer to 300 to raise realistic expectations of an upset. But that doesn't mean the hosts don't have things to think about, especially ahead of a visit to Pakistan and three Tests against Australia, in which a collapse will surely have greater consequences than it did here.

Firdose Moonda is ESPNcricinfo's South Africa correspondent