New Zealand opener Martin Guptill surpassed the Black Caps' highest one-day international score against South Africa with an unbeaten 147 in Hamilton on Wednesday.
Guptill, coming back from a five-week injury layoff, beat Kane Williamson's previous record of 145 against the Proteas in Kimberley in 2013.
His 159-run partnership with Ross Taylor (40) was also New Zealand's highest ever ODI partnership against South Africa.
The pair were still batting as New Zealand were 230 for two late Wednesday chasing South Africa's target of 280.
The Proteas lead the five-match series 2-1, with the Black Caps desperate to level it and set up a winner-takes-all showdown at Auckland's Eden Park on Saturday.