The 19-year-old Gardiner clocked 45.11 seconds beating world decathon record holder Ashton Eaton who posted a new personal best time of 45.55.
Jamaican sprinter Asafa Powell took a confident victory in the men's 100m final clocking 10.01. Saint Kitts and Navis Jason Rodgers was second in 10.23, while Walter Dix of the United States took third.
Jamaican Veronica Campbell-Brown won women's 100m race in 11.22 seconds. Trinidad and Tobago Michelle-Lee Ahye was second in 11.29 while Simone Facey of Jamaica was third in 11.30.
Men's 100m video
In the women's 100m hurdles Queen Harrison (USA) posted 12.84 for the win, while Omar McCleod (JAM) took the men's 110m hurdles in 13.28 beating compatriot Andrew Riley 13.39 and American hurdler Ronnie Ash 13.46.
Defending world 400m champion LaShawn Merritt set the fastest time of the season 31.53 seconds in the 300m race.