After making a steady start to their innings, South Africa suffered setbacks as they lost Tony de Zorzi (12), captain Temba Bavuma (4) and Rassie van der Dussen for a duck in three consecutive overs to lie 39-3 by the end of the ninth.
Rickelton smashed 91 off 102 balls, including three sixes and seven fours, as his partnership with middle-order batter Stubbs got their side back on track.
Rickleton fell in the 35th over and Stubbs six balls later to leave the score 198-5, but with the help of useful knocks from Bjorn Fortuin (28) and Lungi Ngidi (20 not out), South Africa progressed to post a creditable total.
Ireland’s response began poorly as they lost skipper Paul Stirling for two in the first over and while fellow opener Balbirnie, restored to the line-up after sitting out the T20 encounters, and Campher (20), steadied the ship somewhat, the loss of the former saw them sit 38-2 by the end of the ninth over.
Wickets fell regularly thereafter to leave Heinrich Malan’s side 61-5 and, although Dockrell, Andy McBrine (14) and Adair and Young (12 apiece) put up some resistance, the outcome always had an air of inevitability.
Ngidi and Fortuin backed up Williams’ bowling effort with two wickets each.