Ireland 290 for 5 (Balbirnie 102, Tector 79, Phehlukwayo 2-73) beat South Africa 247 (Malan 84, McBrine 2-34) by 43 runs
Dublin: Ireland skipper Andrew Balbirnie says the team showed it is making strides after he scored a century in the first ever win over South Africa.
The Malahide hosts won by 43 runs in the second ODI to take a 1-0 lead going into the final game on Friday.
The Ireland skipper made 102 from 117 balls while Harry Tector added 72 as the hosts posted 290-5.
Janneman Malan (89) and Rassie van der Dussen (49) helped South Africa to 159-2 before they slumped to 247 all out.
South Africa had won the five games, all one-dayers, between the sides before Ireland added the Proteas to their list of big scalps.
Ireland were 195-4 when Sunday's opening ODI was abandoned because of rain and they again impressed with the bat in Dublin after the tourists elected to field first.
Balbirnie made 65 on Sunday and produced another excellent knock after fellow opener Paul Stirling fell for 27.
The captain put on 80 with Andy McBrine (30) and then 70 alongside Tector as the Irish built a strong innings.
Tector and George Dockrell (45) provided a 90-run partnership while Andile Phehlukwayo took 2-73 for the Proteas.
Ireland reduced South Africa to 51-2 before Malan and Van der Dussen added 108 to put the hosts under pressure.
But they lost four wickets for 41 runs as the Ireland bowlers took control before wrapping up the victory in 48.3 overs.
McBrine claimed 2-34 while Mark Adair (2-43) and Josh Little (2-45) also chipped in with two wickets.