Du Plessis, who is leading the side in this series in the absence of the injured AB de Villiers, plundered 111 from 93 balls as South African posted a commanding 361 for six in their 50 overs having been asked to bat by Australia.
The tourists lost regular wickets on a good batting track and were all out for 219 in the 38th over as the home side recorded their second biggest ODI win over Australia by runs, eclipsed only by a 196-run victory a decade ago in Cape Town.
Australia captain Steve Smith inserted South Africa in the belief that bowling conditions would be best in the morning but the home side made a fine start, racing to 70 in the 12th over before Quinton de Kock, who blasted 178 in the first game on Friday, mistimed his shot and was caught for 22.
Fellow opener Rilee Rossouw (75) and JP Duminy (82) made valuable contributions but the innings was steered by Du Plessis’s century as he struck 13 fours and manoeuvred the ball around with great skill.
Australia gave debuts to opening bowlers Chris Tremain and Joe Mennie but they found their introduction to international cricket an eye-opener. Tremain recorded figures of 1-78 in his 10 overs and Mennie finished with 0-82.
John Hastings was the pick of the visiting attack with 3-57 in his 10.
South Africa, in turn, were able to apply pressure with the ball and never let the Australian scoring tempo climb to the required rate.
David Warner (50) and Travis Head (51) were the only batsmen to threaten big scores but they could not convert to three figures to give their side a chance.
Wayne Parnell (3-40 in seven overs) was the most threatening of the home bowlers, while Kagiso Rabada (2-31 in seven) and Imran Tahir (1-31 in seven) the most miserly.
The third ODI will be played in Durban on Wednesday when South Africa will have an early chance to wrap up the series.
(Reporting By Nick Said; Editing by Clare Fallon)
