Neil Wagner says New Zealand failed to exploit helpful bowling conditions on the first day of the second Test against South Africa in Centurion.

Wagner was the pick of the Black Caps attack, taking 2-51 as the home side reached a meritorious 283-3 at stumps at SuperSport Park after being inserted.

New Zealand captain Kane Williamson's decision at the toss was driven by a green pitch which offered plenty of assistance.

However, new ball pair Trent Boult (0-53) and Tim Southee (0-74) were guilty of an inconsistent line and length as the top four South African batsmen all passed 50.

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Left-armer Wagner, who broke the opening stand between the aggressive Quinton de Kock (82) and Stephen Cook (56), said South Africa were let off the hook.

"We didn't start too well with the ball and then later on started bowling better," he said. "We pride ourselves on being a good bowling unit but didn't really do the things we say we're going to do - to bowl in partnerships.

"Sometimes you get it right, sometimes you don't."

Wagner describes the state of the game as evenly-poised but admits the tourists will need early wickets on Sunday, not easily achieved against the well-disciplined Proteas batsmen. JP Duminy is at the crease on 67.

"They showed a lot of patience, they left well and they played the ball really late so there were a lot of nicks that went square of the wicket or didn't carry," he said.

"There was a lot of movement and when we got it in the right areas, there was enough there to keep us interested."

It was an emotional opening day for Pretoria-born Wagner, 30, who has become a key bowler for New Zealand in the last 12 months.

The ground was one where he grew up watching the likes of South African pace bowlers Allan Donald and Shaun Pollock terrorise visiting batsmen.

"I had a lot of goose bumps when I walked out," he said.

"It was the first time in my life when I had my whole family and a lot of my friends that I grew up with setting next to me in the field and watching a Test match.

"It was a special moment for me."