Powerfully built twins Jesse and Dan Kriel will play alongside each other in the midfield for the Baby Boks against the New Zealand Under-20s.
Injury to four players has forced Theron to reshuffle his match 23 after the Junior Boks scored a convincing 61-5 win over Scotland.
Midfielders Rohan Janse van Rensburg (ankle), Andre Esterhuizen (head blow) and flank Jacques Vermeulen (ankle) were all ruled out of selection because of injuries sustained against the Scots.
On Thursday, Golden Lions hooker Malcolm Marx was also ruled out of action for several weeks after he had suffered a knee injury during a training session.
Dan Kriel will now wear the number 12 jersey as stand-in for the powerfully built Esterhuizen.
In the only other change amongst the backs, Blue Bulls scrumhalf JP Smith comes in off the bench for Zee Mkhabela who is now one of the replacements.
Replacement wing Duhan van der Merwe, who joined the squad yesterday from South Africa, is amongst the reserves.
Furthermore, Theron opted for a complete revised front row which now consists of Thomas du Toit, Corniel Els, Dayan van der Westhuizen (props) and Corniel Els (hooker).
Towering lock JD Schickerling got the nod over Abongile Nonkontwana while Jean-Luc du Preez comes in at flank for Vermeulen.
Flyhalf Handré Pollard, who had a sublime match against Scotland, will again lead the Junior Springboks in what is undoubtedly the pick of match day two.
According to Theron, his team knows the huge significance of this vital pool match against New Zealand.
“It is a real pity to have lost four players because of injuries,” the coach said
“We had two very good training sessions on Wednesday and the boys know we are in for an extremely tough encounter against New Zealand,” said Theron.
Commenting on the possible impact of the changes, Theron said: “The players have been training together for a while now and know our system.
“This is a very talented group of players who have worked extremely hard to be here,” according to Theron.
South Africa U20s: 15 Warrick Gelant, 14 Lloyd Greeff, 13 Jesse Kriel, 12 Dan Kriel, 11 Sergeal Petersen, 10 Handré Pollard (captain), 9 JP Smith, 8 Aidon Davis, 7 Cyle Brink, 6 Jean-Luc du Preez, 5 Nico Janse van Rensburg, 4 JD Schickerling, 3 Dayan van der Westhuizen, 2 Corniel Els, 1 Thomas du Toit.
Replacements: 16 Joseph Dweba, 17 Pierre Schoeman, 18 Wilco Louw, 19 Abongile Nonkontwana, 20 Victor Sekekete, 21 Zee Mkhabela, 22 Jean-Luc du Plessis, 23 Duhan van der Merwe.