South Africa, chasing 148 to win at the Wanderers, looked down and out after slumping to 87 for seven after 15 overs. But Parnell scored 29 not out off 11 balls and Theron an unbeaten 30 from 16 deliveries as the tailenders wielded their bats to such good effect that the home side won with five balls to spare to share the two-match series.
Graeme Smith (24) and Johan Botha (34) were the only top-order batsmen to resist the Australian fast bowlers, with James Pattinson (two for 17) and Pat Cummins (two for 26) leading the way.
South Africa’s new-ball pairing of Lonwabo Tsotsobe and Morne Morkel had caused similar problems for the Australian batsmen, reducing them to 17 for two after five overs.
Opening batsman David Warner’s hopes of carrying on his magnificent Champions League form were dashed as he fell for his second successive duck, having a heave at Morkel.
A determined 39 by captain Cameron White partially restored the innings, before a thrilling late onslaught by debutant Mitchell Marsh gave Australia a competitive total of 147 for eight.
All-rounder Marsh showed he has no shortage of batting talent as he lashed 36 off 21 balls, plundering three sixes off the final over of the innings, bowled by Morkel.