Masai Russell of the United States snatched victory in the Olympic women's 100m hurdles on Saturday, edging out France's Cyrena Samba-Mayela in a photo finish.

Russell edged home in 12.33sec to take gold, just a whisker ahead of Samba-Mayela, who clinched the host nation's first athletics medal of the games in 12.34sec.

Puerto Rico's Jasmine Camacho-Quinn took bronze in 12.36sec.

In a thrilling final at the Stade de France, it looked as if home hope Samba-Mayela might have snatched a sensational gold medal after crossing the finish line neck-and-neck with Russell.

But after a brief delay, victory was awarded to Russell by the finest of margins ahead of the Frenchwoman.

Confirmation of Samba-Mayela's silver nevertheless drew one of the loudest roars of the week from the Parisian crowd.

Russell led a powerful US contingent into the final alongside compatriots Alaysha Thompson and US collegiate champion Grace Stark.

But Thompson's challenge faltered after she clipped a hurdle mid-race, leaving a three-way battle for gold with Russell, Samba-Mayela and Camacho-Quinn.