Australia scrambled over the line for a two-wicket victory in the fifth ODI against South Africa to move back to the top of the world rankings less than three months before the World Cup.
What looked like being a stroll to a convincing 4-1 series triumph when Steve Smith departed for 67 with Australia 11 runs from their target of 275 was transformed into a tense finale by Robin Peterson.
The South African spinner (4-32) did most of the damage as the hosts lost four wickets for three runs but James Faulkner held his nerve to smash the winning runs off the first ball of the final over.
Earlier in the afternoon sun, Quinton de Kock's fine 123-ball 107 anchored the South African innings before the opener became Pat Cummins (3-54) third victim when he nicked the ball attempting an uppercut and was caught behind.
Roussouw (51) and Du Plessis (2) had earlier fallen victim to the young Australian quick in one rain-disrupted over.
De Kock's exit left the tourists on 206 for five with just under 10 overs remaining but Farhaan Behardien did his World Cup chances no harm with a blistering career-best 63 from 41 balls to bolster South Africa's tally.
South Africa 280-6 in 50 overs (de Kock 107, Cummins 3-54)
Australia 278-8 in 47.1 overs (D/L) ( Watson 82, Peterson 4-32)