American Richards' time of 50.41 seconds secured her victory in Germany to make up for the disappointment of her failure at the hands of Briton Ohuruogu in Beijing.
Ohuruogu was second, in a time of 50.83 seconds, while Novlene Williams came home in third.
Afterwards the Londoner insisted she was not downbeat by the defeat and it pales into insignificance following her amazing success at the Olympics last month.
"It's nearly the end of my season, and I'm exhausted," she said. "But I'm still glad I came.
"It doesn't mean anything in the overall scheme of things. I have got the biggest accolade in athletics."