The match is a must-win clash for South Africa after the opening ODI was washed out and Ireland shocked their visitors in the second clash, winning by 43 runs.
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Ireland kept the same line-up that won the second ODI while South Africa handed a debut to fast bowler Lizaad Williams.
They also brought back Quinton de Kock and Heinrich Klaasen.
Aiden Markram, David Miller and Kagiso Rabada are the trio to miss out.
Paul Stirling, Andy Balbirnie (captain), Andy McBrine, Harry Tector, George Dockrell, Mark Adair, Curtis Campher, Lorcan Tucker (wkt), Simi Singh, Josh Little, Craig Young
Quinton de Kock, Janneman Malan, Temba Bavuma (captain), Rassie van der Dussen, Kyle Verreynne (wkt), Heinrich Klaasen, Andile Phehlukwayo, Keshav Maharaj, Anrich Nortje, Lizaad Williams, Tabraiz Shamsi