South Africa drops behind India in fourth place, West Indies gains six points to widen gap with eighth-ranked Pakistan.
Matthew Wade, Mitchell Marsh and Josh Hazlewood were the major contributors in the victory.
Darren Bravo hits ton to help West Indies recover after batting collapse, bowlers rattle South Africa to help team win.
Australia are through to the final of the tri-series after a six wicket win. They face the winner of West Indies and South Africa on Thursday.
Australia now face a must win game against West Indies if they want to make it to the final of the tri-series.
The leg spinner claimed 7-45 as South Africa cruised to a 139-run victory against West Indies.
Marlon Samuels produced his best batting effort in ODI against Australia to lead the West Indies to a six-wicket victory in the fifth match of the Tri-Nation series at Warner Park in St Kitts on Monday.
Opener David Warner made his first one-day international (ODI) ton outside Australia to set his team on their way to a 36-run victory over South Africa in the fourth match of the tri-nation ODI series on Saturday.
Dean Elgar has been called up by South Africa to replace injured batsman Rilee Rossouw for the rest of the Tri-Nation One-Day International series in the West Indies, Cricket South Africa said on Wednesday.
Kagiso Rabada led a strong performance with the ball as SA opened their Tri-Nation series account with an emphatic 47-run bonus-point win over Australia at the Guyana National Stadium in Providence on Tuesday.