The US team of Allyson Felix, Tianna Bartoletta, Tori Bowie and English Gardner on Friday clocked 41.04 seconds, beating a fast-finishing Jamaica by 0.35 seconds. Britain was third in 41.77, Xinhua news agency reported.
It was Felix's fifth Olympic gold medal and the third for Bartoletta, who also won the long jump here.
The time was just 19 hundredths of a second slower than the world record set by the US at the London 2012 Games, in which Felix and Bartoletta also participated.
The US originally missed out on qualifying for the final but was allowed a solo re-run of their heat on Thursday when officials ruled it was obstructed during the race.
