Australia took the lead in its swimming showdown against the United States at the Paris Olympics by claiming two of three gold medals on the first full day of competition.Video above: Snoop Dogg carries Olympic torch on its final leg to ParisAriarne Titmus turned one of the most anticipated races of the Games into a blowout when she left Katie Ledecky in her wake at La Defense Arena. Titmus led from start to finish in the 400-meter freestyle Saturday night.The Australian star known as “The Terminator” handed Ledecky a second straight Olympic defeat in an event the American won at Rio de Janeiro in 2016.Titmus faced her stiffest challenge from 17-year-old Canadian phenom Summer McIntosh, but she won comfortably as McIntosh claimed the silver. Ledecky settled for bronze.Titmus swept the 200 and 400 free in Tokyo, and she is going for the same double in Paris. Ledecky is going for …