Having come into the tour having never beaten Australia in any format of the game, South Africa now have a victory against the Aussies in both a T20 International and ODI.
Batting first in a weather interrupted innings, South Africa made 229/6 in 45 overs. Kapp top-scored with a typically swashbuckling knock of 75 (87 balls, 12x4s) batting at number five to help her side post a competitive total.
Tryon ends off Proteas innings in style
With a DLS adjusted target of 234 from 45 overs, Australia began well and put on 22 for the opening partnership from the first four overs.
It was then the turn of Kapp (3/12) with her ruthless pace and movement off the pitch as she removed the top three Aussie batters. That included the delivery of the match which jagged back into to star player Beth Mooney which hurtled into the top of middle stump. A stunned Mooney, who had been a thorn in the side of South Africa so far in this series, was forced to trudge back to the changeroom for a duck.
It also meant the hosts were reduced to 34/3, and they continued to lose wickets regularly until they found themselves 71/8 after 14 overs.
An impressive ninth wicket partnership of 76 between Ashleigh Gardner (35) and Kim Garth (42) restored hopes of an unlikely victory for the favourites, but ultimately Australia were all out for 149.
Ayanda Hlubi (2/41), Eliz-mari Marx (2/22) and De Klerk (2/26) all made strong contributions with the ball after Kapp had set the tone.
The ODI series is now tied at 1-1 heading into the match on Sunday at the same venue.