South Africa has laid the foundations to compile a massive total in Lucknow, largely off the back of a Quinton de Kock century.
The left-handed opener pummelled five sixes alongside eight fours, bringing up three figures in just 90 deliveries, before falling to Glenn Maxwell to finish with 109.
De Kock's second ton of the competition also meant he leapfrogged Mohammad Rizwan (199) as the tournament's highest run-scorer, moving to 209 at an average of 104.50.
The Proteas are positioned at 232/3 with ten overs left in the innings, with Aiden Markram joined by Heinrich Klaasen.
South Africa at one stage looked odds on to reach a total in excess of 350, though a mini fightback from Glenn Maxwell has stemmed the flow of runs a tad.
The off-spinner finished with 2/34 from his ten overs, including a maiden, going all the way through his spell without conceding a boundary.
Maxwell claimed both openers in his effort, while spin partner Adam Zampa ended the stay of Rassie van der Dussen for just 26.
Van der Dussen in the knock passed 2000 runs in ODI cricket in just 45 innings, only bettered by countryman Hashim Amla (40). The right-hander went down the track and tried to slog Zampa over long-on. However, he failed to gain the elevation and was caught by Sean Abbott.
Australia could've had another wicket soon after, but skipper Pat Cummins failed to hold on to a regular chance offered by Aiden Markram off his bowling. De Kock pressed on at the other end, reaching his 19th ODI hundred in the 30th over with a six off Pat Cummins.
The biggest news prior to the game was the selection changes in the Australia camp. Australia skipper Pat Cummins opted to field first in Lucknow. Australia's new-ball pair, Mitchell Starc and Josh Hazlewood, backed his decision in the early overs with some exceptional bowling.
Temba Bavuma tried to pick pace at the other end. He survived some close calls, but the Proteas were up and away.
De Kock reached his 31st ODI half-century in the 16th over. Right after the drinks break, he cracked back-to-back boundaries to help the partnership close in on its 100.
Some disciplined bowling from Australia, helped bring down the scoring rate. It was Glenn Maxwell who got Australia their first breakthrough, when he got the better of Bavuma. The South Africa skipper fell for 35 while going for a big shot.
However, de Kock continued in his aggressive fashion. He hit back-to-back sixes off Josh Hazlewood in the 23rd over.
Australia's two big changes was the big news from the middle at the time of the toss. Marcus Stoinis makes his return to the side after almost three weeks. He replaces Cameron Green in the setup, while wicket-keeper Josh Inglis also made it into the XI in the place of Alex Carey.
For South Africa, Tabraiz Shamsi comes in place of Gerald Coetzee.
Proteas skipper Temba Bavuma believes that the conditions and opposition both played a role in Shamsi's inclusion.
The sides have had contrasting starts to their World Cup campaign. While Australia struggled on a tough track in Chennai and lost to India, South Africa dominated on a flat deck in Delhi to win against Sri Lanka.
