Concussion substitute Marnus Labuschagne played a match-winning innings for Australia to trump an unbeaten century by South African captain Temba Bavuma in the first one-day international at the Mangaung Oval on Thursday.
Bavuma carried his bat for an unbeaten 114 to enable South Africa to score 222 all out.
It seemed more than enough as Australia, batting with ultra-aggressive intent, crashed to 113 for seven in the 17th over.
But Labuschagne, batting at number eight after replacing Cameron Green, restored calmness to the Australian innings, making 80 not out.
He shared an unbeaten eighth-wicket stand of 112 with Ashton Agar, who made 48 not out.
Green was ruled out after being struck on the left earpiece of his helmet by the second ball he faced from Kagiso Rabada before he had scored.
"Some weird things happen around concussions," said man of the match Labuschagne at the after-match presentation.
His Test career was ignited when he replaced Steve Smith during a Test at Lord's in 2019.
Labuschagne was not selected in Australia's World Cup squad and only joined the squad in South Africa after Steve Smith withdrew with a wrist injury.
He said he had taken only a short break after this year's Ashes series in England before getting back to work.
"I knew I needed to improve my one-day game," he said.
Bavuma batted throughout the South African innings while his teammates crumbled against accurate bowling on a slow, dry pitch with uneven bounce.
Bavuma was dropped on two when Agar put down a diving chance at backward point off Sean Abbott.
He survived again on 88, with last man Lungi Ngidi at the wicket, when he top-edged a slog against leg-spinner Adam Zampa and wicketkeeper Alex Carey spilled a straightforward chance.
Two overs later, Bavuma hit Zampa for six and four to raise his fifth one-day international century.
He finished with 14 fours and a six off 142 balls despite struggling with cramp towards the end of the innings.
He watched the Australian innings from the team balcony.
"We weren't at our best with the ball," said Bavuma.
"Marnus took the opportunities he got early on and stabilised the innings."