Canberra: Kyle Abbott and Morne Morkel shared seven wickets after twin ton to helps South Africa beat Ireland by 201-runs at Manuka Oval, Canberra on Tuesday.
This was Ireland first defeat of the World Cup.
Hashim Amla hit 159, Faf du Plessis 109 and Rilee Rossouw a rapid unbeaten 61 in South Africa's 411-4, the second time in two Pool B games they have passed 400.
Ireland never recovered from 48-5 as they were bowled out for 210 in 45 overs despite Andrew Balbirnie's 58.
Kyle Abbott finished with 4-21 and fellow pace bowler Morne Morkel 3-34.
South Africa need to win only one of their remaining two group games, against Pakistan and the United Arab Emirates, to secure a place in the quarter-finals.
Ireland remain well placed to qualify, although the margin of defeat at the Manuka Oval will have a negative impact on their net run rate before Saturday's clash with Zimbabwe in Hobart.
Amla and Du Plessis shared 247, a South Africa record for the second wicket, before Rossouw and David Miller plundered an unbroken 110 off the last 8.3 overs.
Ireland were left to rue two costly drops, Amla put down on 10 by Ed Joyce and Du Plessis, on 19, edging between wicketkeeper Gary Wilson and Kevin O'Brien slip.
Having seen Quinton de Kock fall in the third over, Amla - typically strong through point and mid-wicket - batted with his usual fluency as he became the quickest player to reach 20 ODI centuries.
Du Plessis, whose hundred was equally measured, was finally bowled making room to Kevin O'Brien, and the departure of Amla and De Villiers in the space of three balls merely gave Rossouw and Miller the freedom to mount a late-innings assault.
An improbable Ireland chase became nigh on impossible as Dale Steyn and Abbott shared five wickets in the first 11 overs.
Balbirnie and O'Brien's sixth-wicket stand of 81 helped Ireland avert the heaviest defeat in ODI history, but the remainder of the innings was no more than an exercise in limiting the damage to their net run rate.
Although South Africa employed eight bowlers - including part-timer De Villiers, who removed John Mooney, Morkel mopped up the tail with two wickets in successive overs.
Earlier, unchanged South Africa have won the toss and opted to bat.
Teams:
Ireland: William Porterfield (Capt.), Paul Stirling, Ed Joyce, Niall O'Brien, Andrew Balbirnie, Gary Wilson (wk), Kevin O'Brien, John Mooney, Max Sorensen, George Dockrell, Andy McBrine
South Africa: Hashim Amla, Quinton de Kock (wK), Faf du Plessis, Rilee Rossouw, AB de Villiers (Capt.), David Miller, Farhaan Behardien, Dale Steyn, Kyle Abbott, Morne Morkel, Imran Tahir
Brief scores
South Africa - 411/4 (Amla 159, du Plessis 109, Rossouw 61*)
Ireland - 210 (Balbirnie 58, Abbott 4-21, Morkel 3-34)
Result - South Africa won by 201 runs
Points - South Africa 2, Ireland 0
MOM - Hashim Amla (South Africa)