American Rebecca Soni beat her own world record as she won gold in the women's 200m breaststroke.
The 25-year-old clocked two minutes and 19.59 seconds to become the first swimmer to successfully defend an Olympic title at London 2012 and the first woman to break 2:20.00.
"I've been chasing that for years, that was for my old coach Tom who told me I was going to go that fast," she said.