New Zealand pace bowler Will O'Rourke continued his eye-catching Test debut with two wickets on Thursday as South Africa lost three top-order batsmen before lunch on day three of the second Test.
The visitors were 88-3 in their second innings at the interval Hamilton, having extended their lead to 119 runs.
Zubayr Hamza was on 14 with David Bedingham 34 not out after their unbroken partnership of 49 steadied the innings after O'Rourke snared the wickets of Raynard van Tonder and Neil Brand in quick succession.
The experiment of opening the batting with wicketkeeper Clyde Fortuin again failed when, after struggling to three off 24 balls, he was trapped leg before wicket by spinner Rachin Ravindra.
Lively left-armer O'Rourke took four wickets in South Africa's first innings of 242 before New Zealand were dismissed for 211 at the end of the second day.
His pace and bounce again bothered the Proteas, prompting a mis-timed hook from van Tonder, on one, which went straight to Neil Wagner at fine leg.
South Africa captain and opener Brand had reached 34 when his inside edge off O-Rourke flew to wicketkeeper Tom Blundell.
Bedingham looked the most comfortable, cutting powerfully and scoring four fours and a six.
The under-strength South Africans need a victory to deny New Zealand, who won the first Test by 281 runs, a first Test series victory against the Proteas.