Americans Regan Smith, Lilly King, Kelsey Dahlia and Simone Manuel finished the race with a time of just 3 minutes 50.40 seconds, setting a world record.
In the lead-off leg, Smith set a backstroke world record of 57.57 seconds.
The second-best team was Australia (-3.02 seconds); the Canadian team took third place.
The ladies broke a world record set by another US team (3.51,55).