The 31-year-old was finally caught in the deep off Peterson with Australia needing 38 off the last six overs.
Up till now a spectator to the Watson show, Hussey took on the bowlers and got his side over the line alongside Cameron White (21 not out).
Earlier, Australia meant business after sending South Africa in.
Xavier Doherty (3/20), playing his first game of the tournament, took no time in making his presence felt. He bowled a clueless Richard Levi (0) in the match's opening over before dismissing Jacques Kallis (6) with a typical left-arm spinner delivery. The ball turned enough to induce a slight edge off Kallis' bat which was taken by the wicket-keeper, leaving South Africa at eight for two in the third over.
