Eighteen-year-old Torri Huske finished fourth in the 100m butterfly, just one-hundredth of a second out of bronze medal position, the smallest possible margin in swimming.
Huske was setting world-record pace throughout most of the race, but faded during the final meters. The American finished fourth overall, failing to reach the podium.
Maggie MacNeil of Canada took the gold with a time of 55:59. MacNeil becomes the first Canadian to win an Olympic gold medal in the 100m butterfly.
Zhang Yufei won silver for China and Emma McKeon of Australia took bronze. Only 14 hundredths of a second separated the top four swimmers.
Americans have been on the other side of the .01 margin in past Olympics.
Michael Phelps won a gold in Beijing in 2008 in the 100m butterfly by .01, while Nathan Adrian won the 100m freestyle in London four years later the same way.