It was a seesaw affair from the start, with each side scoring five tries, but in the end, two late penalty goals by Ireland replacement scrumhalf Connor McVicker sealed the deal for his team.
Both teams scored tries in the first 10 minutes, by Ireland hooker and captain Lee Fitzpatrick and SA loosehead prop Jeffrey Singo, both set up by forward dominance.
Ireland took a 12-7 lead with their second try 15 minutes in when Bernard White (centre) crashed over, but the South Africans started finding their rhythm, despite a few mistakes, with their set piece play setting the tone.
With the pressure mounting, Ireland lost Ben Guerin (prop) to the sin bin for repeated infringements close to their tryline, which opened the gap for the hosts to score three tries while they had the numerical advantage.
The SA U18 'A' team took a 14-12 lead when Reinhart Viljoen (fullback) finished a slick move by the backline, and from the restart, they launched an attack down the left-hand touchline, with Viljoen putting Ncutu Kepe (wing) away for a try under the uprights.

Ncutu Kepe goes over for his try.
Both conversions were successful and in to time, the South Africans took a 21-12 lead, but that soon changed to 26-12 when Viljoen scored his second try after taking a quick-tap penalty close to the Irish line.
Unfortunately for the hosts, they let the visitors in for a second maul try on the stroke of half-time, to make it 26-19 at the break.
Ireland scored first in the second half when Fitzpatrick was driven over for his second try, with McVicker's conversion making it 26-26, but a few minutes later, the South Africans converted pressure into points when Lizwe Mthethwa (centre) crashed over, with Uithaler adding the extras to restore a seven-point lead for his team (33-26).
This lead only lasted a minute when White went over for his second try, setting up a tense finale. McVicker and Uithaler traded penalty goals in the last five minutes, before the Irish kicker sealed the deal with his second three-pointer.
Scorers:
SA U18 'A' 33 (26) - Tries: Jeffrey Singo, Reinhart Viljoen (2), Ncutu Kepe, Lizwe Mthethwa. Conversions: Jeandre Uithaler (4). Penalty goal: Uithaler.
Ireland 36 (19) - Tries: Lee Fitzpatrick (2), Bernard White (2), Alex Lautsou. Conversions: Luke Coffey (2), Connor McVicker (2). Penalty goals: McVicker (2).