The Blue Bull added the extra two points and a Springbok counter-attack in the final seconds of the half forced Ma'a Nonu to handle the ball from an offside position, allowing Steyn to give South Africa a nine-point cushion at the interval.
But the game soon descended into an ugly medley of high balls and heavy touches, with Nigel Reo-Coker wasting some decent counter-attacking work from his team-mates with a loose final ball.
She beat Lucie Decosse in the final with a stunning uchi-mata (inner thigh throw) as a counter to the Frenchwoman's own ouchi-gari (inner thigh reap) attack for the maximum ippon score.