Baby Boks make big statement
This followed victories against Wales and Scotland on tour, and Georgia in Cape Town, as part of their World Rugby Under-20 Championship preparations.
The Baby Boks outscored England four tries to two, after leading 14-7 at the break.
"I am very proud," said Roux.
"This was our third match on tour against a fresh English side, and the players showed tremendous character, so all credit to them.
"It was a great team effort. I thought we had the upper hand in the scrums and the line-outs at times, and sometimes they had it, which just shows. But we were lucky to get through it.
"We really showed great character."
With a series of solid performances in the lead-up to the World Rugby U20 Championship, Roux was confident that his charges were on the right track for the international spectacle, which will be hosted in the south of France from 30 May to 17 June.
"This most definitely gives us confidence," said the coach. "We wanted a tough tour with three challenging games, and that is exactly what we got before the tournament."
"It's always disappointing to lose an international but we knew it was going to be a chance for us to try different combinations, give players a first taste of U20 rugby and we have to take those things into consideration as well as the positives from the fixture," England U20 coach Steve Bates said.
"We know what we have to work on.
"Fair play to South Africa, they were very physical, they played well in the first half and drove the line-out well, but when at half-time we solved that problem we gave a good account of ourselves. They scored a late intercept try so we have to be too careful not to judge things solely on the scoreline.
"This will be far more useful for us than having a 50-point victory over lesser opposition. This will stand us in good stead heading into the World Rugby U20 Championship and will also be useful for us to refer back to when we go to France."
The first half against England was tightly fought as both packs tried to create a solid platform, while the backs fed off this to make their presence felt.
The Junior Springboks struck first with a try in the opening minutes by wing David Kriel and fullback Gianni Lombard converted to hand the team a 7-0 lead. Lombard received a yellow card shortly after for an illegal tackle, and England took advantage of this as wing Ben Loader forced his way through the defence out wide to level the scores.
The hard grind continued between the packs in the following exchanges, but it was the SA U20 team that made the most of this, as scrumhalf Rewan Kruger dotted down after some good forward pressure, which pushed the visitors 14-7 ahead.
The SA U20 team extended their lead to 19-7 thirteen minutes into the second half as hooker Schalk Erasmus crossed the chalk from a rolling maul, and the team continued to apply pressure on attack as the match progressed.
England closed the gap on the scoreboard to 19-12 in the 65th minute as Henry Walker scored the team's second try. But this was cancelled out later on as Junior Springbok centre and man-of-the-match Rikus Pretorius scored an intercept try with six minutes left on the clock to stretch their lead to 26-12.
England fought hard until the end, but the visitors' solid defence shut them out, and they wrapped up the victory.
The Junior Springboks will return to South Africa for their World Rugby U20 Championship holding camp before departing for France on May 25.
For England U20:
For SA U20:
Tries:Kriel, Kruger, Erasmus, Pretorius
Cons: Lombard 3
England U20: 15 Tom Parton (London Irish), 14 Tom Seabrook (Gloucester), 13 Ollie Lawrence (Worcester Warriors), 12 Fraser Dingwall (Northampton Saints), 11 Ben Loader (London Irish), 10 James Grayson (Northampton Saints), 9 Ben White capt (Leicester Tigers), 8 Tom Willis (Wasps), 7 Aaron Hinkley (Gloucester), 6 Ted Hill (Worcester Warriors), 5 James Scott (Worcester Warriors), 4 Joel Kpoku (Saracens), 3 Joe Heyes (Leicester Tigers), 2 Gabriel Oghre (Wasps), 1 Alex Seville (Gloucester).
Replacements: 16 Henry Walker (Gloucester), 17 Toby Trinder (Northampton Saints), 18 Ehren Painter (Northampton Saints), 19 Sam Lewis (Leicester Tigers), 20 Josh Basham (London Irish), 21 Rory Brand (London Irish), 22 Sam Morley (Exeter Chiefs), 23 Luke James (Sale Sharks).
South Africa U20: 15 Gianni Lombard (Golden Lions), 14 David Kriel (Western Province), 13 Wandisile Simelane (Golden Lions), 12 Rikus Pretorius (Western Province), 11 Tyrone Green (Golden Lions), 10 David Coetzer (Western Province), 9 Rewan Kruger (Free State), 8 Muller Uys (Western Province), 7 PJ Steenkamp (Western Province), 6 Dian Schoonees (Golden Lions), 5 Ben-Jason Dixon (Western Province), 4 Salmaan Moerat (captain Western Province), 3 Sazi Sandi (Western Province), 2 Schalk Erasmus (Western Province), 1 Nathan McBeth (Golden Lions).
Replacements: 16 Daniel Jooste (Western Province), 17 Tiaan van der Merwe (Golden Lions), 18 Asenathi Ntlabakanye (Golden Lions), 19 Phendulani Buthelezi (Sharks), 20 Ruan Nortje (Blue Bulls), 21 Jack Hart (Golden Lions), 22 Lyle Hendricks (Western Province), 23 Sihle Njezula (Western Province).
Referee: Elgan Williams (Wales)
Catch the Junior Springboks take on @EnglandRugby at 20h30 SA time tonight on livestreaming on https://t.co/La5qL0kwHG This marks their final warm-up match before the World Rugby U20 Championship @Springboks pic.twitter.com/V2csnIGKEe
— Junior Springboks (@JuniorBoks) May 11, 2018