Williamson reeled off an unbeaten 133 to see the Black Caps to a seven-wicket victory at Seddon Park and a 2-0 clean sweep over a weakened Proteas squad.

The former skipper scored almost exactly half of the 267-run target, once again underlining his reputation as one of the calmest chasers around.

The hosts had resumed on 40 for one and saw spinner Dane Piedt take two wickets in the morning session before Will Young forged a decisive stand with the former skipper.

Piedt had Tom Latham caught by Zubayr Hamza for 30 and Rachin Ravindra by stand-in skipper Neil Brand for 20, taking his match tally to eight wickets on comeback.

From there, Williamson defied some variable bounce to convert his 32nd Test hundred in a six-hour knock as Young chipped in an important 60 not out.

The result extended New Zealand's lead at the summit of the World Test Championship table.