But SA hit back with their first try of the second half when Lange went over from close quarters for his third five-pointer, converted by Donovan Don, which took the lead to 33-8 with plenty of time left to play.
Hartzenberg grabbed his second when he won the foot race to a brilliant grubber by Steyn and Don converted brilliantly to take the score to 40-8 with 20 minutes to go.
Five minutes later, it was 47-8 when outside centre Ethan James waltzed through to score under the posts, while Don again added the extras.
It was the last score for the Junior Boks as Wales finished with three late tries by reserve fullback Joe Westwood, flanker Ethan Fackrell and reserve prop Cameron Jones.
Scorers
Junior Springboks (26) 47
Tries: Louw Nel, Tiaan Lange (3), Suleiman Hartzenberg (2), Ethan James. Conversions: Sacha Mngomezulu (3), Donovan Don (3).
Wales U-20 (3) 27
Tries: Mason Grady, Joe Westwood, Ethan Fackrell, Cameron Jones. Conversions: Joe Hawkins (2). Penalty: Hawkins
Junior Boks captain Mngomezulu praises team after Six Nations series win
Image: Ben Brady/INPHO/Shutterstock/BackpagePix
Junior Springbok captain Sacha Mngomezulu was full of praise for his teammates after they beat Wales 47-27 to win the Six Nations Under-20 Summer Series in Treviso on Tuesday night.
Mngomezulu said playing in the U-20 Summer Series was a dream come true for the players and they were rewarded for their hard work.
The win over Wales on Tuesday ensured SA U-20 were the only team to leave Italy unbeaten, having beaten England, Ireland and France in the pool stages.
“The boys worked extremely hard and they deserve this,” said Mngomezulu, who is in the books of the Sharks.
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“Credit must also go to the coaches who made us work hard and put in such a good effort for us to be ready. It’s an amazing feeling standing here unbeaten after four games.
“Not so long ago we didn't even play rugby so credit must go to World Rugby and the Six Nations for staging this excellent tournament. They allowed the boys to create lifelong memories.”
Coach Bafana Nhleko's team were impressive in the opening half where they dominated the kicking game and possession as the Welsh struggled with the physicality of the Junior Boks.
Replacement hooker Tiaan Lange scored three of the South Africans' seven tries and if it wasn't for lapses in concentration late in both halves from the Junior Boks, the victory could have been bigger.
No 8 Louw Nel went over in the corner after a quick tap penalty for the first try of the match in the sixth minute with Mngomezulu adding the conversion from the side to hand the SA U-20s a 7-0 lead.
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Wales skipper Joe Watkins landed his first points when he nailed a penalty goal from the restart, but in the next move SA hooker Lukhanyo Vokozela was injured with Wales prop Nathan Evans yellow-carded for a dangerous tackle.
From the ensuing lineout, Lange – who had just replaced Vokozela – scored the second try that was converted by Mngomezulu to stretch the Junior Boks' lead to 14-3.
In the 22nd minute, inside centre Suleiman Hartzenberg scored a brilliant try when he sliced though the Welsh defence from a lineout to score under the posts.
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With the score at 21-3, the SA U-20s looked settled and in control, and they went further ahead a few minutes later when Lange went over for his second try.
Shortly thereafter, Mngomezulu was forced to leave the field with an arm injury, with Neil le Roux coming on at scrumhalf and Nico Steyn moving to flyhalf.
The Junior Boks were reduced to 14 men when Nel was yellow-carded for foul play, which cost the SA U-20s some momentum.
Wales drew first blood in the second half when their outside centre Mason Grady outpaced the Junior Boks defence to score out wide, reducing SA's lead to 26-8.
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But SA hit back with their first try of the second half when Lange went over from close quarters for his third five-pointer, converted by Donovan Don, which took the lead to 33-8 with plenty of time left to play.
Hartzenberg grabbed his second when he won the foot race to a brilliant grubber by Steyn and Don converted brilliantly to take the score to 40-8 with 20 minutes to go.
Five minutes later, it was 47-8 when outside centre Ethan James waltzed through to score under the posts, while Don again added the extras.
It was the last score for the Junior Boks as Wales finished with three late tries by reserve fullback Joe Westwood, flanker Ethan Fackrell and reserve prop Cameron Jones.
Scorers
Junior Springboks (26) 47
Tries: Louw Nel, Tiaan Lange (3), Suleiman Hartzenberg (2), Ethan James. Conversions: Sacha Mngomezulu (3), Donovan Don (3).
Wales U-20 (3) 27
Tries: Mason Grady, Joe Westwood, Ethan Fackrell, Cameron Jones. Conversions: Joe Hawkins (2). Penalty: Hawkins
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