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Masai Russell won by the slimmest of margins in the women's 100-meter hurdles.
The American needed a lunge on her final stride of the race to beat out France's Cyrena Samba-Mayela for gold.
Russell pulled off the upset over Tokyo gold medalist Jasmine Camacho-Quinn, who settled for bronze.
Russell became the third American to win the event in the last six Olympics and she continued the Team USA streak of at least one medalist in the event in every Games dating back to Sydney in 2000.