Graeme Smith hit an unbeaten 68 as South Africa completed a series whitewash over Bangladesh to move make to the top of the world rankings.
Chasing just 144 for victory in the third and final one-day international in Mirpur, the Proteas romped to victory with more than 15 overs remaining.
Captain Smith led the way with a classy half-century, with AB de Villiers weighing in with 40 as South Africa reached the target with seven wickets in hand.
And the win means South Africa pass Australia in the one-day standings.
Earlier Albie Morkel had set South Africa on their way with a four-wicket haul.
The 26-year-old finished with 4-29, having started the Bangladesh collapse on the ninth over.
The hosts, having won the toss and elected to bat, had reached 34-0 before Morkel had Tamim Iqbal caught behind by back-up wicketkeeper de Villiers.
Top-scorer Shahriar Nafees (25) and Mohammad Ashraful quickly followed, while the departure of Mohammad Nazimuddin saw Bangladesh slump to 72-4.
The wickets continued to tumble, with only Farhad Reza's unbeaten 20 offering much resistance as off-spinner Johan Botha claimed 3-34.