Plum
I think De Kock's problem was he knew that team selection for the Proteas was a sham. and the team was designed to lose. That he was forced to deal with the losers as captain demoralized him.
There were some subtle changes made in this test - such as moving Van der Dussen from the slips into the open field and putting Mulder in the slips instead,
Once De Kock became sure that the lunacy was discontinued he flourished. The only problem in this test was really Elgar. As captain he did consult with De Kockk on bowling changed and field placings - as a batsman he failed. The latter is factual in any match eh ahd to face quality bowling - that is why his first class average is way below what is expected from a .test quality opening batsman.
I was not impressed by the batting performances of Petersen and Verreiy ne - but one has to bear in mind that in his first ten innings Kallis batted for the test team his average was below 15 runs per innings, Inexperience could account for them losing their wickets early - but that excuse cannot be for Elgar,
The players who impress me most in this test were de Kock, Markram, Mulder (in batting and fielding), Nortje ( not only in bowling - but also in fielding), Ngidi and Rabada, One could add Van der Dussen to the list as well - but he was in the main defensive and his run-scoring was painfully slow.