Quinton de Kock hit a brilliant 174, his third century of the World Cup, as South Africa piled up 382-5 against Bangladesh at the Wankhede Stadium in Mumbai on Tuesday.
The Proteas were briefly in trouble at 36-2 after winning the toss but rallied strongly, taking 144 runs off the last 10 overs.
But left-handed opener De Kock responded with a third hundred in five World Cup innings -- after scores of 100 and 109 against Sri Lanka and Australia -- as he continued his superb start to what the 30-year-old has said will be his last major one-day tournament.
Heinrich Klaasen followed up with a blistering 90 just days after his 109 in South Africa's 229-run thrashing of reigning champions England at the Wankhede amid soaring heat and humidity on Saturday.
All of Bangladesh's seven-stong attack suffered as Bangladesh bowling coach and former South Africa spearhead Allan Donald looked on, none more so than new-ball paceman Mustafizur Rahman whose nine wicketless overs cost 76 runs.
Fit-again Bangladesh captain Shakib Al Hasan, appearing in his fifth World Cup, was not spared either during a return of 1-69 in nine.
South Africa briefly faltered after Bangladesh's early double strike but De Kock and stand-in captain Aiden Markram (60) then shared a stand of 131.
It was no surprise when Markram, again leading South Africa while regular captain Temba Bavuma remained sidelined by illness, decided to bat first upon winning the toss given the Proteas posted a mammoth 399-7 after being sent in by England.
South Africa were faltering after Reeza Hendricks and Rassie van der Dussen fell in quick succession.
Markram was in fine touch until he tamely chipped Shakib to long-off.
But De Kock completed his 20th hundred in 150 ODIs before, in sight of becoming just the third batsman to score a World Cup double century, he sliced Hasan Mahmud to deep backward point.
He faced 140 balls in total, including 15 fours and seven sixes.
Klaasen ensured there was no respite with eight sixes in his 49-ball innings before he holed out in the last over.
South Africa have won three of their opening four World Cup matches, with the only blot on their record a shock loss to non-Test side the Netherlands.
Bangladesh are struggling to qualify for the semi-finals following three defeats in four games.
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