South Africa captain Dean Elgar won the toss and elected to bat at Hagley Oval, with his team looking to bounce back from their second-worst Test defeat in the series-opener at the same ground.
He and fellow opener Erwee managed only 11 between them in the first Test but were rock-solid against probing pace and seam throughout a sunny morning session on Friday.
Playing in his second Test, lefthander Erwee brought up his 50 in the final over before lunch, driving all-rounder Colin de Grandhomme to the fence.
He was 53 not out at the break, with Elgar on 25.
New Zealand lead the two-Test series 1-0 after completing a thumping innings and 276-run win last week.
South Africa made three changes, bringing in all-rounder Wiaan Mulder, spinner Keshav Maharaj and paceman Lutho Sipamla.
Batsman Zubayr Hamza was ruled out with a fractured thumb, while pace bowlers Duanne Olivier and Glenton Stuurman were dropped.
Out-of-form No.3 Aiden Markram was spared the axe.
"It's important for us to front up," Elgar said at Hagley Oval after the toss.
"The wicket looks a lot better than the first Test.
"It's maybe not a bad thing to front up as a batting unit and hopefully get a respectable target."
New Zealand, missing captain Kane Williamson and pace spearhead Trent Boult, stuck with the same 11 who were dominant in the series-opener as they look to complete their first-ever series win over the Proteas.
"We would've bowled as well," said stand-in captain Tom Latham.
While a draw will be enough for New Zealand to win the series, victory would see them dislodge Australia as the world's No.1 Test side, while shoring up their World Test Championship defence with maximum points.
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