Sanya Richards-Ross of the United States won the women's Olympic 400 metres title at the third time of asking on Sunday in 49.55 seconds.
Britain's defending champion Christine Ohuruogu came into the home straight in seventh but put on a late spurt to snatch the silver on the line by 0.02 seconds from American DeeDee Trotter in 49.70.
Botswana's world champion Amantle Montsho finished fourth.
Richard-Ross set off at a blisering pace but was behind Russian Antonina Krivoshapka and Trotter coming off the final bend.
With a determined look on her face, the 27-year-old, who has overcome a series of health problems, kept her form to reel them in, smiling as she dipped for the line.
Richards-Ross has 4x400 relay golds from 2004 and 2008 but this was her first individual title.
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