The left-handed De Kock thrashed 178 off 113 balls, with 16 fours and 11 sixes, as South Africa made a challenging target of 295 look easy. The hosts won with 13.4 overs to spare.
"He was magnificent," Australian captain Steve Smith said of De Kock. "It was a 370-380 wicket if you look back at it now. Someone (for Australia) had to get a big hundred like Quinton did."
De Kock and stand-in fellow opener Rilee Rossouw put an inexperienced Australian pace bowling attack to the sword in an opening partnership of 145 off 104 balls before Rossouw missed a reverse sweep against the first ball bowled by leg-spinner Adam Zampa and was leg before wicket for 63, made off 45 balls.
He then found himself in the starting team today when Hashim Amla was ruled out by illness.
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De Kock was in imperious form virtually from the start of his innings, hitting a six off John Hastings in the second over. He reached 50 off 38 balls and reached his 11th one-day international century off 74 balls when he pulled Daniel Worrall for his fourth six.
"During the evening the ball comes on nicely," said De Kock. "Me and Rilee didn't have to do anything extravagant."
It was an opinion which the Australians and everyone else at Centurion might not agree with.
"At night it's difficult to defend," said South African captain Faf du Plessis. "But that doesn't take anything away from Quinton."
De Kock broke a favourite bat during his innings but shrugged it off. "Wood is wood," he said.
against Ireland last Sunday, Phehlukwayo was hit for 16 runs in his first over by Aaron Finch but came back strongly.
He had Finch caught at backward square leg and Smith leg before wicket in his second over. He followed up with the wicket of Mitchell Marsh, caught by a diving wicketkeeper De Kock.
George Bailey and John Hastings dug Australia out of a trouble with a 79-run stand after they had been in danger of not batting out their overs when they slipped to 192 for six in the 29th over.
With David Warner setting the tone with 40 off 36 balls, Australia scored rapidly after being sent in but kept losing wickets before Bailey and Hastings came together.