Shaunae Miller-Uibo of the Bahamas won the gold medal, with Marileidy Paulino of the Dominican Republic taking silver.
Felix, 35, passed the record of Jamaica’s Merlene Ottey, who won nine Olympic medals.
Felix has now won six golds, three silvers and one bronze.
She has the chance of an 11th medal on Saturday, when the United States seek to defend their 4x400m relay title, and it would take her past Carl Lewis as the most decorated American track and field athlete. (Courtesy BBC)