Before carving out an international career in New Zealand, fast bowler Wagner learnt his cricket at Pretoria's Afrikaans' Boys High School, the nursery that produced South Africa internationals AB de Villiers and Faf du Plessis.
Top order batsman Elgar was schooled at St Dominic's College in Welkom near Bloemfontein, and shared a number of fiery encounters with Wagner in their junior days and also at provincial level more than a decade ago.
"Free State against Northerns -- it used to be pretty feisty," Elgar told New Zealand media in Dunedin on Monday, ahead of the series-opener at the University Oval.
"There's a lot of Afrikaans people in those two teams and it was pretty heated. It was all in good spirit and I guess we were all playing for careers we never thought we could have back then."
Both have since become valued cricketers for their national sides while developing a firm friendship off the field.
The pair met at test level last August in the washed-out series-opener in Durban and also at Port Elizabeth in 2013, which South Africa won by a crushing margin.
"We've had a lot of battles on the field as young boys, from school cricket going onwards, we hated playing against each other," the 30-year-old Wagner said.
"But Dean is a great man. I do like sitting afterwards having a beer with him but, yeah, we hate playing against each other. I guess it is part and parcel of the job."
If selected, left-armer Wagner will hope to help his adopted New Zealand improve on its dismal record of only four wins from the previous 42 test matches against South Africa. The Proteas, by contrast, have won 24.
The last time the sides played at University Oval in 2012, the Proteas were frustrated by rain that washed out day five, having set the home side a big target and removed both openers.
In seven tests at the venue, New Zealand have won three and never been beaten.
"Good for them, I guess," the 29-year-old Elgar said. "It's something for us to try and correct.
"It's a very non-South African style of cricket we need to play and we need to find our niche very soon. We need to adapt, assess the conditions as soon as possible and try to throw the first punch."
(Writing by Ian Ransom; Editing by John O'Brien)
