Ricky Ponting conceded Australia had been consistently outplayed by South Africa after the Proteas concluded their tour with a 39-run win in Perth.
The victory, set up by a patient 97 from opener Hashim Amla, sealed a 4-1 one-day series rout for South Africa, who displace Australia at the top of the International Cricket Council's ODI rankings.
The Proteas also claimed a maiden Test series win on Australian soil earlier in the tour.
"I guess it's a disappointing way for us to end this series," Ponting said.
"The South Africans have totally outplayed us right the way through."
The Proteas posted 288-6 on the back of Amla's contribution, while AB de Villiers and JP Duminy, arguably the two touring batsmen to enhance their reputations the most in Australia, chipped in with scores of 60.
Australia's run chase was immediately undermined when they lost in-form duo Shaun Marsh (5) and Ricky Ponting (12) to debutant Lonwabo Tsotsobe. The left-armer eventually finished with figures of 4-50.
And while a patient 78 from Mike Hussey and some late hitting from Brad Haddin (63) gave Australia faint hope, they always remained behind the required rate before eventually being bowled out for 249 from 48.5 overs.
It was the third consecutive game that the hosts had been bowled out and, after the first three games went down to the wire, Ponting was disappointed with the way his team finished the series.
"I thought we were competitive in the first three games but our last two performances have been well below par and we haven't played well enough to win," he added.
"We made a lot of mistakes, whether it be with the ball in the field or our batting."
South Africa captain Johan Botha reserved special praise for the younger members of his team, who excelled at the WACA in the absence of the likes of Jacques Kallis, Dale Steyn and Makhaya Ntini.
Tsotsobe and Wayne Parnell made their debuts while Vaughn van Jaarsveld earned just his second cap.
"We had a lot of young players in the team and they gave a good performance," Botha said.
"We had quite a young team but they put their hands up.
"I thought the guys played really nicely during the series, everyone contributed.
"I think the tight moments in the game went our way, which we are really happy about.
"The young players came in and put in some good performances and that's what you want to see."