Richardson, the silver medallist in the women's 100 metres sprint at the 2024 Paris Olympics behind Saint Lucia's Julien Alfred, was the fortunate beneficiary of a false start in Monday's final after a slow getaway at the first attempt.
The 26-year-old American needed the full 120 metre stretch to reel in race leader Charlotte Nielsen, who was in front with about 30 metres left to travel.
"She's come from the clouds!" cried legendary broadcaster Bruce McAvaney as Richardson became the third athlete in the 37-year history of the women's event to win from the back of the track.
Richardson reportedly commands a six-figure appearance fee at some high-profile athletics meetings and received a comparatively modest prize of AU$40,000 for her victory.
It is not known publicly whether Richardson, nor her boyfriend sprinter Christian Coleman who was the marquee recruit of the men's event but failed to qualify for the event after also starting off scratch, were paid by organisers for their time at the Stawell Gift.
Sha'carri had a much cleaner run on Monday than her weekend semi-final and credited a "patient first ten metres" for her victory.
"I think I realised I was going to win right past 90 (metres)," Richardson told the broadcast.
"This is one of the most exciting, fun, and entertaining track meets I've ever ran in.
"The true love and support for track and field is unbeatable."