The conditions made handling difficult, but the South African pack laid the foundation for a solid win against the 2022 Six Nations and Grand Slam champions, outscoring their opponents by five tries to three, with the final Irish try coming after the hooter had sounded.
With England beating France earlier on the day, the SA U20s now lead Pool A with a full-house of 10 points, followed by the English and French on five points each, while the Irish are yet to open their account.
The Junior Boks dominated the opening half and led 26-3 through four tries and three conversions, while the Irish could only reply with a penalty goal. The Irish hit back with three converted tries in the second period, while the SA U20s managed one converted try for their second win in a row.
Bafana Nhleko, the Junior Springbok coach, said that while he was happy with the result, he wasn't too pleased with the number of unforced errors.
"Very pleased for the boys because they won against a good side who are the Six Nations U20 champions," said Nhleko.
"The Irish showed their quality, especially in the second half. It was another great learning opportunity for the boys, and I thought we did well to manage the game despite their persistent pressure."
The Junior Springbok started strongly when they earned a scrum penalty as early as the third minute. Skipper Sacha Mngomezulu steered his effort agonisingly left.
Three minutes later they earned a reward for another strong scrum performance when Cameron Hanekom (No 8) crossed the line for the first try of the evening. Mngomezulu slotted the conversion to take the score to 7-0.
Ireland had to wait until halfway through the opening half before flyhalf Sam Prendergast earned their first points with a succesful penalty kick.
The SA U20s were powerful in the collisions and were rewarded with turnovers, but several unforced errors threathened to spoil their hard work.
However, the Junior Boks stretched their lead to 12-3 when industrious lock Reinhardt Ludwig was at hand to take a final pass to force his way over for the second five pointer of the first half, but the conversion wasn't successful.
Sniffing dominance upfront, the pack won another huge collision and with the penalty kicked to the corner, it was no surprise when Tiaan Lange (hooker) went over for the third try of the opening stanza, which Mngomezulu converted as they increased their advantage to 19-3.
Not long after Lange's try, Corne Rahl (lock) went over the whitewash to take the halftime score to 26-3.
With Lange in the bin though, Ireland were rewarded for a good passage of play just after the restart with Dylan O’Grady scoring under the sticks.
Replacement hooker Lukhanyo Vokozela made his presence felt with a try shortly after coming on, with his skipper adding the extras to take the Junior Boks' lead back to 23 points at 33-10.
Ireland hit back with a converted try from replacement prop Oisin Michel as they narrow the gap to 33-17 halfway through the second half, and Reuben Crothers scored on fulltime to take the final score to 33-24.
The Junior Boks tackle France next week Tuesday in their third outing, with the match set to kick off at 17h00.
Junior Springboks 33 (26) - Tries: Cameron Hanekom, Reinhardt Ludwig, Tiaan Lange, Corne Rahl, Lukhanyo Vokozela. Conversions: Sacha Mngomezulu (4).
Ireland 24 (3) - Tries: Dylan O’Grady, Reuben Crothers, Oisin Michel. Conversions: Sam Prendergast (2), Reece Malone. Penalty goal: Prendergast.