After winning their pool games against England, Ireland and France, the SA Under-20s were pitted against Wales in the series finale, with the Junior Boks impressive as they won their fourth game on the trot in Italy.
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.
Junior Springbok captain Sacha Mngomezulu said afterwards playing in the U20 Summer Series was a dream come true for him and the team.
"The boys worked extremely hard and they deserve this," said Mngomezulu.
"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 too long ago, we didn't even play rugby, so credit to World Rugby and the Six Nations for staging this excellent tournament. They allowed the boys to create life long memories," added the Junior Bok skipper.
Bafana Nhleko's team were impressive in the opening half, dominating the kicking game and possession, while the Welsh struggled with the South African physicality.
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. Mngomezulu added the conversion from the side to hand the SA U20s a 7-0 lead.
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, also converted by Mngomezulu, to stretch the Junior Boks' lead to 14-3.
The SA kicking game gave them positional advantage, while their defence was also solid whenever the Welsh threatened.
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.
With the score at 21-3, the SA U20s looked settled and in control, and they went even 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 then reduced to 14 men when Nel was yellow carded for foul play, all of which cost the SA U20s some momentum.
Wales drew first blood in the second half when their outside centre Mason Grady outpaced the Junior Boks defence to score our wide, reducing the South Africans' lead to 26-8.
But South Africa 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 then grabbed his second when he won the foot race to a brilliant grubber by Steyn. Don converted brilliantly 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.
But the night belonged to the Junior Boks who simply had too much class.
Junior Springboks 47 (26) - Tries: Louw Nel, Tiaan Lange (3), Suleiman Hartzenberg (2), Ethan James. Conversions: Sacha Mngomezulu (3), Donovan Don (3).
Wales U20 27 (3) - Tries: Mason Grady, Joe Westwood, Ethan Fackrell, Cameron Jones. Conversions: Joe Hawkins (2). Penalty goal: Hawkins.