Caitlin McClatchey finished seventh in the 200 metres freestyle final in a race which was won by Allison Schmitt in Olympic record time.
Former double Commonwealth champion McClatchey touched in 1min 57.60secs in what is set to be her final Olympics after three Games.
Schmitt, who last month swam the event faster than anyone in textiles in history, led from start to finish and touched in a dominant one minute 53.61 seconds.
France's Camille Muffat was second as the pair reversed their placings in the 400m freestyle on Sunday.