In ominous news for New Zealand, South African batsman Faf du Plessis believes the Proteas have been operating at barely two-thirds of their capacity in their current one-day international series.
With the ODI series poised at two games apiece, du Plessis says there's huge room for improvement from South Africa going into Saturday's decider in Auckland.
The South Africans need to win the clash at Eden Park in order to regain to the world number-one ranking after slipping behind Australia following their loss in Hamilton on Wednesday.
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"I think we've been firing at about 65 per cent this whole series," the South African Test captain said.
"We haven't played close to a complete game at all.
"In all skills, we've just been a little bit off the boil - we haven't been consistent enough."
Du Plessis says South Africa have been unable to build hundreds from their top six batsmen, and have struggled to put big totals on the board.
With the ball, he is looking for South Africa's young bowlers to be more relentless in the areas they target.
"We've been very soft in giving boundaries away," he said.
"They need to become a little bit smarter in the areas they bowl, start creating that real pressure pocket in the game where as a batter you feel the squeeze and feel like you have to do something out of the ordinary to create something."
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Du Plessis said neither side had delivered consistently good cricket across the five-match ODI series.
"I don't think both teams have played their best cricket," he said.
"It's been a series where it hasn't been dominated by the bat - the bowlers have played a huge part.
"I think both teams will feel they're a little bit under-performing."
Meanwhile, off-spinner Jeetan Patel has been recalled to the Black Caps squad for the first Test against the Proteas in Dunedin next week.
Selector Gavin Larsen said Patel's variety was the primary reason for his call-up.
"Jeetan brings the ability to spin the ball away from the left-handers, which complements our other spinner in Mitchell Santner nicely," Larsen said.
"He brings a huge amount of experience to the team and gives us the balance of having two front-line spin options."
Allrounder Jimmy Neesham has been recalled to the 13-strong squad and Neil Wagner has also returned, a month after dislocating a finger.
Wicketkeeper BJ Watling also returns, after taking a month off to rest a knee injury.
Matt Henry and Dean Brownlie drop out of the squad and will play in the Plunket Shield day-night match beginning next week.
There was no room for Martin Guptill, despite his match-winning 180 not out in the fourth ODI on Wednesday.
NZ Test squad: Kane Williamson (captain), Trent Boult, Colin de Grandhomme, Tom Latham, Jimmy Neesham, Henry Nicholls, Jeetan Patel, Jeet Raval, Mitchell Santner, Tim Southee, Ross Taylor, Neil Wagner, BJ Watling