The 37-year-old off-spinner hit an unbeaten 27 while helping to add 40 runs for the last wicket with Allan Donald to lift South Africa's total to 200 off 50 overs.
And then he took four for 28 off 10 overs as a new-look Australia, captained by Steve Waugh, collapsed to 133 all out in 38 overs.
Symcox had complained to the umpires that the crowd were pelting him with oranges and tennis balls, and play was stopped for five minutes to clear up the outfield.
Part-time spinner Daryll Cullinan picked up two for 31, helping topple Australia, missing Test captain Mark Taylor, from the seemingly strong position of 61 for one. Opener Mark Waugh top-scored with 45.
South Africa were set for a below-par score after some tight Australian bowling, particularly by Glenn McGrath, who returned from a groin injury to finish with three for 40.