Mullings sprinted to first place in a photo finish in 10.26 seconds like Gay but a closer look revealed Mullings had crossed the line just ahead of the American runner.
Trinidad and Tobago Keston Bledman’s was third in a time of 10.33.
“I still got a lot to learn,” said Mullings. “I’ve never been in a championship running the 100 meters. I don’t know what it feels like to be in a championship final in the 100. That’s what I’m working on, to be up there with those guys.”