Captain Brendon McCullum on Thursday acknowledged that New Zealand will be judged on their performance against South Africa, not Zimbabwe.

Dominant in the one-off Test, three ODIs and the first of the two Twenty20 Internationals against the minnow Zimbabweans earlier this month, the Black Caps head into a much tougher three-T20I, three-ODI, three-Test affair against the Proteas, starting with Friday's first T20I in Wellington.

Bar the final T20I, which they almost lost before Kane Williamson's late-innings blitz saved them from defeat, the Kiwis brushed aside a Zimbabwean unit largely out of their depth in New Zealand. South Africa, however, are only two spots lower than McCullum's men in the Twnety20 rankings and far superior on the ODI and Test table.

"We got a bit giddy in some of our options and executions in the last game against Zimbabwe and it wasn't our best game over the last few weeks, but I'm confident we can step up in the coming days and play at the level needed to beat South Africa," insisted McCullum, leading the side in the absence of the injured Ross Taylor.

"We know we're going to be judged on how we go in this series and the opportunity to start the series in the form of the game we're quite strong is a positive for us.

"If we want to continue to improve as an international team, become consistent and move up the rankings in all three forms, then you've got to beat the good teams and do it consistently. That's the challenge in front of us. But it's also an opportunity, so we're pretty excited.

"Our focus is very much on making sure we start this series well. It's a big series for us and the New Zealand public is desperate to get in behind us at the moment and we've had a pretty good start to our season."

The Kiwis deployed as many as four spinners against Zimbabwe, with part-timers Williamson and Rob Nicol partnering specialists Nathan McCullum and Ronnie Hira across the two T20Is. With seamer Jacob Oram sidelined by injury and the conditions at Westpac Stadium likely to suit the slow bowlers, McCullum anticipated a similar attack against AB de Villiers' men come Friday's clash.

"That's one of the areas we think we're reasonably strong in and hopefully if we can give our spinners the opportunity to get into the game early, they'll be able to settle into their work and put them under some pressure. If the pitch is a bit greener then what we think we'll have to assess it, but at this stage we're looking to play Ronnie for sure," he added.

"We're still a little bit cautious on Oram, so we'll give him another game out of the 12, then hopefully he'll be back for the next one in Hamilton on Sunday."