The series is hosted by SA Rugby at Paul Roos Gymnasium’s Markötter Stadium, and is supported by World Rugby, Rugby Africa and UK Sport, with R10 the title sponsor.
Earlier on Friday, Uganda fought back from 17-0 down against Tunisia but the North Africans held on for a 17-14 victory.
However, the day belonged to the South Africans, who showed their class as they negated a fast start by the Rhinos to follow up their victory on Monday over Tunisia with another win, scoring seven tries to two in the process.
Rhinos flanker Neidene Solomons scored in the sixth minute, but the South Africans then took control, which they held for most of the game.
With the wind in their backs, the South African forwards were in dominant form - with Dineo Ndhlovu (lock), Sinothile Bhengu (prop) and Sinoxolo Soga (No 8) setting the tone - while Melissa Younie controlled proceedings from flyhalf.
The SA U20s dished up some good play in the first half, but unfortunately they made a few mistakes in the Rhinos' 22, which cost them points.
South Africa scored their first try after 11 minutes when Bhengu burst through a few tackles after they showed good attacking patience. Younie's conversion gave the hosts a 7-5 lead.
A superb 50-22 kick by Younie set up the second try, by Doney Filies (fullback), with the Junior Bok Women playing with composure. The SA U20 flyhalf converted and at 14-5 after 18 minutes, they were firmly in control.
It took them 22 minutes for a third try though, when Soga went over from a quick-tap penalty, with Younie keeping her 100% kicking record in tact with the conversion.
The Rhinos drew first blood in the second half when Kwanele Zungu (centre) went over after a strong carry and some good handling, but a few minutes later Robyn Strydom scored under the sticks from a clever box kick into space.
Soga and Bhengu then added second tries to their tallies as the Rhinos' defence could not handle the strong-running from the Junior Boks, and with 20 minutes to go, South Africa were firmly in control at 38-10.
Hard-working flanker Emihle Mayitshe added her name to the score sheet with 10 minutes to go, but at this stage the Boland heat was taking its toll as more mistakes crept into play on both sides. Zungu wrapped up proceedings with her second try after a great counter-attacking move from inside the Rhinos' half.
The R10 African U20 Women’s Series concludes on Tuesday, when the Rhinos square off against Tunisia, and the Junior Bok Women take on Uganda.
Scorers:
Junior Springbok Women 43 (21) - Tries: Sinothile Bhengu (2), Doney Filies, Sinoxolo Soga (2), Robyn Strydom, Emihle Mayitshe. Conversions: Melissa Younie (4).
San Clemente Rhinos 15 (5) - Tries: Neidene Solomons, Kwanele Zungu (2).