The home side were sent in to bat in Durban and posted 164 for eight in their 20 overs, a total that never looked enough with the small boundaries at Kingsmead.

Australia had little trouble knocking off their target in 14.5 overs as Marsh followed up his unbeaten 92 in the 111-run victory in the first match on Wednesday with 79 not out from 39 deliveries, including eight fours and six sixes.

He put on 100 in 45 balls for the second wicket with impressive opener Matthew Short, who was both elegant and brutal in equal measure for his 66 from 30 balls.

It was a maiden international half-century for Short after he debuted in the first game of the series.

"It's great, I’m proud of the boys because a series win in South Africa is hard to come by," Marsh said at the post-match presentation.

"Tonight the game was set up by the bowlers, they were all fantastic."

Home skipper Aiden Markram was the top scorer in South Africa’s innings with 49 from 38 balls after opener Temba Bavuma was fast out of the blocks with 35 off 17.

But Australia picked up wickets at regular intervals with some clever changes of pace and swing on a helpful wicket.

Seamers Shaun Abbott (3-22) and Nathan Ellis (3-25) were the pick of their bowlers, with Jason Behrendorff chipping in with a handy 2-25.

"Temba got us off to a great start but the loss of (regular) wickets made it challenging," Markram said. "We wanted to take it deep. When they came on to bat it can be hard when there are two batters trying to muscle it out of the ground."

The final match in the series is at the same venue on Sunday before the teams switch formats for a five-game One-Day International series ahead of the World Cup that starts in India next month.