In the evening, Americans Michael Phelps and Ryan Lochte are scheduled to line up for a classic confrontation in the men's 400 metres individual medley final.
Phelps, competing in seven events after winning a record eight gold medals four years ago in Beijing, is bidding to become the first swimmer to win gold in the same discipline three times in a row.
"This is going to be a special race," said Gregg Troy, head coach of the American men's team. "I can't imagine a better way to promote our sport than a race like this on the first day."
Image: South Korea's Im Dong-Hyun collects his arrows during an individual ranking round at the 2012 Summer Olympics, Friday, July 27, 2012, in London. Dong-Hyun set world record in the round with a 699 score.