Their 66-run sixth wicket partnership, dominated by de Grandhomme’s half-century, lifted New Zealand to 157 for five at stumps in reply to South Africa’s 364.
Playing with the lights on during a gloomy afternoon at Hagley Oval, South Africa had New Zealand at five for 91 before de Grandhomme joined Mitchell in the middle.
The burly all-rounder favoured attack as the best defence and was not out at 54 off 61 deliveries at stumps, with the more circumspect Mitchell on 29.
After being outplayed on day one, New Zealand battled back into the reckoning on the second morning with four wickets for 60, to have South Africa 298 for seven at lunch.
Day 2 in the books at Hagley Oval. Another strong day for South Africa. Colin de Grandhomme 54* Daryl Mitchell 29*… https://t.co/sOdUkpWaoD
— BLACKCAPS (@BLACKCAPS) 1645855276000
Two overs after the resumption, South Africa were 302 for eight but then, following a 20-minute rain disruption, the momentum swung back the Proteas’ way.
Marco Jansen and Keshav Maharaj mounted a rollicking 62-run stand off 78 deliveries — a record ninth wicket partnership for South Africa against New Zealand — and South Africa were back in the box seat.
When Kyle Jamieson eventually mopped up the tail, New Zealand’s situation worsened.
Kagiso Rabada removed openers Tom Latham for nought and Will Young for three, both caught behind — and New Zealand were two down for just nine runs.
Devon Conway and first Test century-maker Henry Nicholls attempted to put some backbone into the innings, although Conway never looked at ease.
Just like that Colin de Grandhomme has 50 at Hagley Oval from just 36 balls. Follow play LIVE from Christchurch wit… https://t.co/9ByuLOYqr5
— BLACKCAPS (@BLACKCAPS) 1645852874000
He was given a hard time by Rabada who had an lbw appeal turned down and dropped a sharp caught-and-bowled chance before Jansen claimed the wicket with Kyle Verreynne taking another legside catch.
South Africa lost two reviews appealing for leg-before decisions before eventually getting the fourth wicket with a carefully laid plan to catch Nicholls for 39.
Jansen delivered a tempting short, wide delivery similar to one which Nicholls had cut for four early in his innings.
He could not resist slashing again — but this time Sarel Erwee was waiting at backward point for the catch.
Tom Blundell lasted six balls for six runs before he was bowled by Rabada, who has figures of three for 37, while Jansen has two for 48.
New Zealand had the measure of South Africa before lunch with Matt Henry and Neil Wagner taking two wickets each.
Henry removed Temba Bavuma for 29 and Verreynne for four in the space of 10 deliveries, and Wagner claimed the wickets of Rassie van der Dussen for 25 and Wiaan Mulder for 14.
But after Wagner dismissed Rabada for six after lunch Jansen and Maharaj regained control for the tourists.
They were particularly harsh on Wagner, taking 39 including seven fours in five overs, before the South African-born New Zealander was taken out of the attack.
He was replaced by Jamieson who wrapped up the innings in his first over with the dismissal of Maharaj for an entertaining 36 off 50 deliveries, while Lutho Sipamla went without scoring and Jansen was left unbeaten on 37.
Wagner returned figures of four for 102 while Henry took three for 90.