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Video - Steffen swims to second win
Germany's Britta Steffen held off 41-year-old Dara Torres by a hundredth of a second to win the women's 50m freestyle in an Olympic record time.
Steffen, who had already won the 100m, finished in 24.06 seconds to shatter Inge de Bruijn's eight-year-old record.
American Torres earned the silver in 24.07 for her 11th career medal in her fifth Olympic Games.
Australian Cate Campbell, 16, was third while her compatriot, world record holder Libby Trickett, was fourth.
"In the first 20m I noticed Dara Torres beside me," Steffen said. "My coach told me the last 10 metres would decide the results."
Torres, whose silver in the 4x100m free relay in Beijing had already made her the oldest Olympic swimming medallist, quipped: "I'm thinking I shouldn't have filed my nails last night."