South Africa, who won the toss and chose to bat, were 85 for one at lunch on the first day.
Smith, who missed the third test against Australia because of a finger injury, was 41 not out with Boeta Dippenaar on 31 in a stand of 69 for the unbroken second wicket.
Smith and Herschelle Gibbs opened the batting, but were separated in the fifth over when Gibbs (six) played to an inswinger from seamer Kyle Mills and edged the ball onto his middle stump.
Smith and Dippenaar batted steadily for the rest of the session on a pitch that offered bounce but not much movement off the seam.
Dippenaar was in fluid form, hitting six fours from the 65 balls he faced. A more circumspect Smith faced 84 balls and hit five boundaries.
Stephen Fleming became the first New Zealander to reach 100 test caps, while allrounders Jacques Kallis and Shaun Pollock joined retired opening batsman Gary Kirsten as the only South Africans to reach the milestone.
Fast bowler Dale Steyn was included in the South African team after Andre Nel was ruled out with a shoulder injury.
New Zealand fast bowler Shane Bond failed a fitness test on his swollen knee, which brought Mills into the match.
Mills had figures of one for 14 from seven overs.