With AB de Villiers rested for the third one-day international in Bulawayo on Thursday, Du Plessis took over captaincy duties and oversaw a convincing seven-wicket triumph.
Elton Chigumbura made 90 in Zimbabwe's 165 all out, before 84 from Quinton de Kock and 40 from Du Plessis helped the tourists - who rested Hashim Amla - ease to victory.
With a triangular series against Zimbabwe and Australia to come, Du Plessis is gearing himself up for what will surely be a tougher test against Michael Clarke's side.
"We started the series thinking about beating Zimbabwe convincingly and to win 3-0, we are very happy," he said.
"Today it was nice for me to express myself as there was no Hash [Amla]. With Hash, you don't need to score boundaries.
"Australia is coming and they are a really powerful team. It will be a nice challenge for us."
De Kock's innings earned him the man of the match award, with his 185 runs across all three games enough for him to clinch the man of the series prize to boot.
"It's good, I am enjoying every moment of it," he said. "I don't really plan much. I go to nets and hit a couple of balls, then I see how the game pans out."
Losing skipper Chigumbura, meanwhile, believes there are positives to take from the series as Zimbabwe look ahead to the World Cup in Australia and New Zealand next year.
"[John] Nyumu bowled well throughout the series," he said. " [Prosper] Utseya and [Sean] Williams did very well. Williams did very well with the bat throughout too.
"We are looking forward to the World Cup and we wanted to have a look at a few guys."