De Kock showed sparkling strokeplay in a brisk 82 as he and Stephen Cook became the first opening pair to feature in a 100-run partnership for South Africa since December 2013.
Cook scored 56, Hashim Amla 58 and JP Duminy was 67 not out at the close along with captain Faf du Plessis (13).
Left-hander De Kock had been sent up the batting order after Dean Elgar suffered a freak ankle injury on the eve of the test, and he punished the loose balls as he cracked 10 fours on his way to 50.
He was first man out after lunch, however, pulling Neil Wagner and being caught by Trent Boult on the boundary to end a first-wicket stand of 133.
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Cook went 20 runs later, taken in the gully by New Zealand captain Kane Williamson’s low catch off the bowling of Doug Bracewell.
Amla survived a close lbw decision when on 17 to reach his 31st test half century before Wagner bowled one that held its line and took an edge to be snapped up by wicketkeeper BJ Watling.
Duminy was given out lbw when he was on 44 but stayed after successfully reviewing the decision. With his place in the test side under threat when AB de Villiers returns from injury, he will be hoping to get to his century when play resumes on Sunday.
New Zealand won the toss and sent South Africa into bat on surface that did not provide the bowlers with expected assistance. Wagner had the best return of 2-51 off 22 overs.
The outcome of this test will settle the two-match series after the first was drawn last week when the majority of playing time was lost to a wet outfield in rain-hit Durban.
(Editing by Ed Osmond)
