Matt Grevers led a US one-two finish in the men's 100m backstroke on Monday, capturing gold in an Olympic record of 52.16sec.
Grevers, second at the turn behind world champion Camille Lacourt, edged ahead with about 25m remaining and drove for the final wall.
Behind him the French swimmer faded, leaving American Nick Thoman, swimming out in lane two, and Japan's Ryosuke Irie to battle it out for silver.
Thoman came through in 52.92sec with Irie claiming bronze in 52.97.
The victory was a validation for Grevers, who earned silver behind Aaron Peirsol in the 100m back in Beijing but failed to qualify for the 2010 Pan Pacific Championships or the 2011 world championships in Shanghai.