South Africa won the third and final ODI in Potchefstroom by six wickets.
Proteas restricted the visitors to a modest total of 254/7 in 50 overs despite Marnus Labuschagne's century (108), with Anrich Nortje (2/35) and JJ Smuts (2/42) taking a couple of wickets each.
In the run-chase, De Kock (26) and fellow opener Janneman Malan (23) got their team off to a decent start before half-centuries from Smuts (84), Kyle Verreynne (50) and Heinrich Klaasen (68*) guided the side through.
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"Very proud of the boys, we played very well this series," captain De Kock said at the post-match presentation ceremony. "Makes me really proud. That's what we've been asking from the team, a bit of consistency, congrats to the guys."
De Kock's captaincy tenure has begun on a wonderful note with four wins in six games against England and Australia this home summer. "It's (captaincy) been good, it's been quite busy, the guys have helped me out a lot," he said. "It's not too much on my shoulder at the moment, it's been good. We didn't start well, but this series win reminds us how good we can play. We didn't play bad cricket."
A series win against a major opponent in the new dawn with young players leading the way augurs well for the future.
"Guys like Kyle stepped. Guys like Klaasen and Malan have shown that they belong to this level. We are not going to take anything for granted when we go there (India). We are not a finished product at the moment. We'll just keep working," De Kock added.
For Australian captain Aaron Finch, however, the feeling was of despair as the visitors went down heavily for the third consecutive time on the tour.
Australia's middle-order failed to stitch substantial partnerships and the team's bowling unit couldn't put enough pressure on the opposition batting line-up.
"We haven't been at our best. We have been good in patches, (and then) let the foot off the gas," Finch said. "Credit to South Africa, they put us under a lot of pressure with both bat and ball. A tough series. We have to do our basics well. We would have liked to get more runs."
Overdependence on experienced heads in the batting line-up like Steve Smith, David Warner and the skipper himself was brutally exposed in the series loss.
"Our top three with the experience of myself, Warner and Smith, to not get a big score hangs on us," Finch added. "All round, we haven't been at our best. It's a quick turnaround (to the next series versus New Zealand), there'll be a few tired boys. It's going to be a busy time, but you're playing for Australia, what else would you want to do."
(Inputs from Cricbuzz)