Having already lost to Australia, New Zealand and England earlier in the series, the Proteas showed improvement but went down 68-36 against the Diamonds.
In one of their better quarters of the series, the Proteas put on an impressive show for the first 15 minutes of the game, briefly taking a 5-4 lead before the Australians called a short break, upped their workrate and re-grouped to take a 19-9 lead at the end of the first quarter, before stretching clear for a comfortable win.
"We wanted to keep the goal difference under 20 goals but we showed some good progress on court today," said Proteas captain Amanda Mynhardt.
"We could have capitalised more on our turnovers, but defensively we did well with a lot of good balls and intercepts."
South Africa next play New Zealand in Tauranga on Sunday.